mangos: remove dependency on mangos/v2 (#188)

Fixes #187

Author: sbinet

Diff for: go.mod

@@ -4,7 +4,7 @@ require (
 	github.com/Microsoft/go-winio v0.4.11
 	github.com/gdamore/optopia v0.2.0
 	github.com/gorilla/websocket v1.4.1
-	nanomsg.org/go/mangos/v2 v2.0.8
+	golang.org/x/sys v0.0.0-20181128092732-4ed8d59d0b35 // indirect
 )
 
 go 1.13

Diff for: go.sum

@@ -4,8 +4,5 @@ github.com/gdamore/optopia v0.2.0 h1:2t3+oyTrJ9e0jxmXqeacws1SFKu4eIrg+U87GjtlA8M
 github.com/gdamore/optopia v0.2.0/go.mod h1:YKYEwo5C1Pa617H7NlPcmQXl+vG6YnSSNB44n8dNL0Q=
 github.com/gorilla/websocket v1.4.1 h1:q7AeDBpnBk8AogcD4DSag/Ukw/KV+YhzLj2bP5HvKCM=
 github.com/gorilla/websocket v1.4.1/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
-go.nanomsg.org/mangos v2.0.0+incompatible h1:Ll6GIzeGGld6/bFrVgBB8CjwibhHXZtF5jon+GoH1bE=
 golang.org/x/sys v0.0.0-20181128092732-4ed8d59d0b35 h1:YAFjXN64LMvktoUZH9zgY4lGc/msGN7HQfoSuKCgaDU=
 golang.org/x/sys v0.0.0-20181128092732-4ed8d59d0b35/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-nanomsg.org/go/mangos/v2 v2.0.8 h1:Nnc5gCNPd8sSyxgfMTdlKK020p4nxLAxcQrhLVnjGQ8=
-nanomsg.org/go/mangos/v2 v2.0.8/go.mod h1:gngxudWUZkxqHN+8n/2y9gWZPcwmSbliFYJsYG8mbKs=