set Go version to 1.15 and run go mod tidy

go.mod

 module github.com/libp2p/go-socket-activation
 
-go 1.13
+go 1.15
 
 require (
 	github.com/coreos/go-systemd/v22 v22.0.0

go.sum

@@ -5,44 +5,22 @@ github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 github.com/godbus/dbus/v5 v5.0.3/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/gogo/protobuf v1.2.1 h1:/s5zKNz0uPFCZ5hddgPdo2TK2TVrUNMn0OOX8/aZMTE=
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
-github.com/gxed/hashland/keccakpg v0.0.1 h1:wrk3uMNaMxbXiHibbPO4S0ymqJMm41WiudyFSs7UnsU=
-github.com/gxed/hashland/keccakpg v0.0.1/go.mod h1:kRzw3HkwxFU1mpmPP8v1WyQzwdGfmKFJ6tItnhQ67kU=
-github.com/gxed/hashland/murmur3 v0.0.1 h1:SheiaIt0sda5K+8FLz952/1iWS9zrnKsEJaOJu4ZbSc=
-github.com/gxed/hashland/murmur3 v0.0.1/go.mod h1:KjXop02n4/ckmZSnY2+HKcLud/tcmvhST0bie/0lS48=
-github.com/ipfs/go-log v1.0.1 h1:5lIEEOQTk/vd1WuPFBRqz2mcp+5G1fMVcW+Ib/H5Hfo=
-github.com/ipfs/go-log v1.0.1/go.mod h1:HuWlQttfN6FWNHRhlY5yMk/lW7evQC0HHGOxEwMRR8I=
-github.com/ipfs/go-log v1.0.2 h1:s19ZwJxH8rPWzypjcDpqPLIyV7BnbLqvpli3iZoqYK0=
-github.com/ipfs/go-log v1.0.2/go.mod h1:1MNjMxe0u6xvJZgeqbJ8vdo2TKaGwZ1a0Bpza+sr2Sk=
 github.com/ipfs/go-log v1.0.3 h1:Gg7SUYSZ7BrqaKMwM+hRgcAkKv4QLfzP4XPQt5Sx/OI=
 github.com/ipfs/go-log v1.0.3/go.mod h1:OsLySYkwIbiSUR/yBTdv1qPtcE4FW3WPWk/ewz9Ru+A=
-github.com/ipfs/go-log/v2 v2.0.1 h1:mnR9XFltezAtO8A6tj5U7nKkRzhEQNEw/wT11U2HhPM=
-github.com/ipfs/go-log/v2 v2.0.1/go.mod h1:O7P1lJt27vWHhOwQmcFEvlmo49ry2VY2+JfBWFaa9+0=
-github.com/ipfs/go-log/v2 v2.0.2 h1:xguurydRdfKMJjKyxNXNU8lYP0VZH1NUwJRwUorjuEw=
-github.com/ipfs/go-log/v2 v2.0.2/go.mod h1:O7P1lJt27vWHhOwQmcFEvlmo49ry2VY2+JfBWFaa9+0=
 github.com/ipfs/go-log/v2 v2.0.3 h1:Q2gXcBoCALyLN/pUQlz1qgu0x3uFV6FzP9oXhpfyJpc=
 github.com/ipfs/go-log/v2 v2.0.3/go.mod h1:O7P1lJt27vWHhOwQmcFEvlmo49ry2VY2+JfBWFaa9+0=
 github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/minio/blake2b-simd v0.0.0-20160723061019-3f5f724cb5b1 h1:lYpkrQH5ajf0OXOcUbGjvZxxijuBwbbmlSxLiuofa+g=
 github.com/minio/blake2b-simd v0.0.0-20160723061019-3f5f724cb5b1/go.mod h1:pD8RvIylQ358TN4wwqatJ8rNavkEINozVn9DtGI3dfQ=
-github.com/minio/sha256-simd v0.0.0-20190131020904-2d45a736cd16 h1:5W7KhL8HVF3XCFOweFD3BNESdnO8ewyYTFT2R+/b8FQ=
-github.com/minio/sha256-simd v0.0.0-20190131020904-2d45a736cd16/go.mod h1:2FMWW+8GMoPweT6+pI63m9YE3Lmw4J71hV56Chs1E/U=
 github.com/minio/sha256-simd v0.1.1-0.20190913151208-6de447530771 h1:MHkK1uRtFbVqvAgvWxafZe54+5uBxLluGylDiKgdhwo=
 github.com/minio/sha256-simd v0.1.1-0.20190913151208-6de447530771/go.mod h1:B5e1o+1/KgNmWrSQK08Y6Z1Vb5pwIktudl0J58iy0KM=
-github.com/mr-tron/base58 v1.1.0 h1:Y51FGVJ91WBqCEabAi5OPUz38eAx8DakuAm5svLcsfQ=
-github.com/mr-tron/base58 v1.1.0/go.mod h1:xcD2VGqlgYjBdcBLw+TuYLr8afG+Hj8g2eTVqeSzSU8=
 github.com/mr-tron/base58 v1.1.2 h1:ZEw4I2EgPKDJ2iEw0cNmLB3ROrEmkOtXIkaG7wZg+78=
 github.com/mr-tron/base58 v1.1.2/go.mod h1:BinMc/sQntlIE1frQmRFPUoPA1Zkr8VRgBdjWI2mNwc=
-github.com/multiformats/go-multiaddr v0.1.0 h1:fkISCUNDb3xIpCcI6BGlPsQE+ywcxzimOsUnHWnrE74=
-github.com/multiformats/go-multiaddr v0.1.0/go.mod h1:xKVEak1K9cS1VdmPZW3LSIb6lgmoS58qz/pzqmAxV44=
 github.com/multiformats/go-multiaddr v0.2.0 h1:lR52sFwcTCuQb6bTfnXF6zA2XfyYvyd+5a9qECv/J90=
 github.com/multiformats/go-multiaddr v0.2.0/go.mod h1:0nO36NvPpyV4QzvTLi/lafl2y95ncPj0vFwVF6k6wJ4=
-github.com/multiformats/go-multiaddr-net v0.1.1 h1:jFFKUuXTXv+3ARyHZi3XUqQO+YWMKgBdhEvuGRfnL6s=
-github.com/multiformats/go-multiaddr-net v0.1.1/go.mod h1:5JNbcfBOP4dnhoZOv10JJVkJO0pCCEf8mTnipAo2UZQ=
 github.com/multiformats/go-multiaddr-net v0.1.2 h1:P7zcBH9FRETdPkDrylcXVjQLQ2t1JQtNItZULWNWgeg=
 github.com/multiformats/go-multiaddr-net v0.1.2/go.mod h1:QsWt3XK/3hwvNxZJp92iMQKME1qHfpYmyIjFVsSOY6Y=
-github.com/multiformats/go-multihash v0.0.1 h1:HHwN1K12I+XllBCrqKnhX949Orn4oawPkegHMu2vDqQ=
-github.com/multiformats/go-multihash v0.0.1/go.mod h1:w/5tugSrLEbWqlcgJabL3oHFKTwfvkofsjW2Qa1ct4U=
 github.com/multiformats/go-multihash v0.0.8 h1:wrYcW5yxSi3dU07n5jnuS5PrNwyHy0zRHGVoUugWvXg=
 github.com/multiformats/go-multihash v0.0.8/go.mod h1:YSLudS+Pi8NHE7o6tb3D8vrpKa63epEDmG8nTduyAew=
 github.com/multiformats/go-varint v0.0.1 h1:TR/0rdQtnNxuN2IhiB639xC3tWM4IUi7DkTBVTdGW/M=
@@ -64,15 +42,11 @@ go.uber.org/multierr v1.1.0 h1:HoEmRHQPVSqub6w2z2d2EOVs2fjyFRGyofhKuyDq0QI=
 go.uber.org/multierr v1.1.0/go.mod h1:wR5kodmAFQ0UK8QlbwjlSNy0Z68gJhDJUG5sjR94q/0=
 go.uber.org/zap v1.10.0 h1:ORx85nbTijNz8ljznvCMR1ZBIPKFn3jQrag10X2AsuM=
 go.uber.org/zap v1.10.0/go.mod h1:vwi/ZaCAaUcBkycHslxD9B2zi4UTXhF60s6SWpuDF0Q=
-golang.org/x/crypto v0.0.0-20190211182817-74369b46fc67 h1:ng3VDlRp5/DHpSWl02R4rM9I+8M2rhmsuLwAMmkLQWE=
-golang.org/x/crypto v0.0.0-20190211182817-74369b46fc67/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190611184440-5c40567a22f8 h1:1wopBVtVdWnn03fZelqdXTqk7U7zPQCb+T4rbU9ZEoU=
 golang.org/x/crypto v0.0.0-20190611184440-5c40567a22f8/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190219092855-153ac476189d h1:Z0Ahzd7HltpJtjAHHxX8QFP3j1yYgiuvjbjRzDj/KH0=
-golang.org/x/sys v0.0.0-20190219092855-153ac476189d/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5/tI9ujCIVX+P5KiHuI=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=