dep: switch back to upstream pubsub

In preparation for switching over to go modules entirely. We no longer need our
fork.

go.mod

 module github.com/ipfs/go-bitswap
 
 require (
+	github.com/cskr/pubsub v1.0.2
 	github.com/gogo/protobuf v1.2.1
-	github.com/gxed/pubsub v0.0.0-20180201040156-26ebdf44f824
 	github.com/hashicorp/golang-lru v0.5.1
 	github.com/ipfs/go-block-format v0.0.2
 	github.com/ipfs/go-cid v0.0.1

go.sum

@@ -12,6 +12,8 @@ github.com/btcsuite/websocket v0.0.0-20150119174127-31079b680792/go.mod h1:ghJtE
 github.com/btcsuite/winsvc v1.0.0/go.mod h1:jsenWakMcC0zFBFurPLEAyrnc/teJEM1O46fmI40EZs=
 github.com/coreos/go-semver v0.2.0 h1:3Jm3tLmsgAYcjC+4Up7hJrFBPr+n7rAqYeSw/SZazuY=
 github.com/coreos/go-semver v0.2.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=
+github.com/cskr/pubsub v1.0.2 h1:vlOzMhl6PFn60gRlTQQsIfVwaPB/B/8MziK8FhEPt/0=
+github.com/cskr/pubsub v1.0.2/go.mod h1:/8MzYXk/NJAz782G8RPkFzXTZVu63VotefPnR9TIRis=
 github.com/davecgh/go-spew v0.0.0-20171005155431-ecdeabc65495/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -37,8 +39,6 @@ github.com/gxed/hashland/keccakpg v0.0.1 h1:wrk3uMNaMxbXiHibbPO4S0ymqJMm41WiudyF
 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/gxed/pubsub v0.0.0-20180201040156-26ebdf44f824 h1:TF4mX7zXpeyz/xintezebSa7ZDxAGBnqDwcoobvaz2o=
-github.com/gxed/pubsub v0.0.0-20180201040156-26ebdf44f824/go.mod h1:OiEWyHgK+CWrmOlVquHaIK1vhpUJydC9m0Je6mhaiNE=
 github.com/hashicorp/golang-lru v0.5.1 h1:0hERBMJE1eitiLkihrMvRVBYAkpHzc/J3QdDN+dAcgU=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hpcloud/tail v1.0.0 h1:nfCOvKYfkgYP8hkirhJocXT2+zOD8yUNjXaWfTlyFKI=

notifications/notifications.go

@@ -4,7 +4,7 @@ import (
 	"context"
 	"sync"
 
-	pubsub "github.com/gxed/pubsub"
+	pubsub "github.com/cskr/pubsub"
 	blocks "github.com/ipfs/go-block-format"
 	cid "github.com/ipfs/go-cid"
 )

package.json

@@ -56,10 +56,10 @@
       "version": "0.2.0"
     },
     {
-      "author": "why",
-      "hash": "QmdbxjQWogRCHRaxhhGnYdT1oQJzL9GdqSKzCdqWr85AP2",
+      "author": "cskr",
+      "hash": "QmPKLamJq9Z2apKJVCVXZ5aYNrWiFk5HTKjmEbU16Qjdcd",
       "name": "pubsub",
-      "version": "1.0.0"
+      "version": "1.0.2"
     },
     {
       "author": "hsanjuan",