chore(dep): update btc (sekp) and openssl libraries

* The btc (sekp crypto) library now uses go mod.
* Our openssl library now supports a few more platforms.

go.mod

 module github.com/libp2p/go-libp2p-core
 
 require (
-	github.com/btcsuite/btcd v0.0.0-20190824003749-130ea5bddde3
+	github.com/btcsuite/btcd v0.20.1-beta
 	github.com/coreos/go-semver v0.3.0
 	github.com/gogo/protobuf v1.3.1
 	github.com/ipfs/go-cid v0.0.3

go.sum

@@ -2,8 +2,8 @@ cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMT
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/aead/siphash v1.0.1 h1:FwHfE/T45KPKYuuSAKyyvE+oPWcaQ+CUmFW0bPlM+kg=
 github.com/aead/siphash v1.0.1/go.mod h1:Nywa3cDsYNNK3gaciGTWPwHt0wlpNV15vwmswBAUSII=
-github.com/btcsuite/btcd v0.0.0-20190824003749-130ea5bddde3 h1:A/EVblehb75cUgXA5njHPn0kLAsykn6mJGz7rnmW5W0=
-github.com/btcsuite/btcd v0.0.0-20190824003749-130ea5bddde3/go.mod h1:3J08xEfcugPacsc34/LKRU2yO7YmuT8yt28J8k2+rrI=
+github.com/btcsuite/btcd v0.20.1-beta h1:Ik4hyJqN8Jfyv3S4AGBOmyouMsYE3EdYODkMbQjwPGw=
+github.com/btcsuite/btcd v0.20.1-beta/go.mod h1:wVuoA8VJLEcwgqHBwHmzLRazpKxTv13Px/pDuV7OomQ=
 github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f h1:bAs4lUbRJpnnkd9VhRV3jjAVU7DJVjMaK+IsvSeZvFo=
 github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f/go.mod h1:TdznJufoqS23FtqVCzL0ZqgP5MqXbb4fg/WgDys70nA=
 github.com/btcsuite/btcutil v0.0.0-20190425235716-9e5f4b9a998d h1:yJzD/yFppdVCf6ApMkVy8cUxV0XrxdP9rVf6D87/Mng=
@@ -67,9 +67,9 @@ github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/libp2p/go-flow-metrics v0.0.3 h1:8tAs/hSdNvUiLgtlSy3mxwxWP4I9y/jlkPFT7epKdeM=
 github.com/libp2p/go-flow-metrics v0.0.3/go.mod h1:HeoSNUrOJVK1jEpDqVEiUOIXqhbnS27omG0uWU5slZs=
-github.com/libp2p/go-openssl v0.0.3 h1:wjlG7HvQkt4Fq4cfH33Ivpwp0omaElYEi9z26qaIkIk=
-github.com/libp2p/go-openssl v0.0.3/go.mod h1:unDrJpgy3oFr+rqXsarWifmJuNnJR4chtO1HmaZjggc=
 github.com/libp2p/go-openssl v0.0.4 h1:d27YZvLoTyMhIN4njrkr8zMDOM4lfpHIp6A+TK9fovg=
+github.com/libp2p/go-openssl v0.0.4 h1:d27YZvLoTyMhIN4njrkr8zMDOM4lfpHIp6A+TK9fovg=
+github.com/libp2p/go-openssl v0.0.4/go.mod h1:unDrJpgy3oFr+rqXsarWifmJuNnJR4chtO1HmaZjggc=
 github.com/libp2p/go-openssl v0.0.4/go.mod h1:unDrJpgy3oFr+rqXsarWifmJuNnJR4chtO1HmaZjggc=
 github.com/mailru/easyjson v0.0.0-20180823135443-60711f1a8329 h1:2gxZ0XQIU/5z3Z3bUBu+FXuk2pFbkN6tcwi/pjyaDic=
 github.com/mailru/easyjson v0.0.0-20180823135443-60711f1a8329/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=