Build gost after go1.8.3, so go 1.8.3 can be used in the build. (#133)

snapcraft.yaml

-name: gost # you probably want to 'snapcraft register <name>'
-version: '2.4' # just for humans, typically '1.2+git' or '1.3.2'
+name: gost
+version: '2.4'
 summary: GO Simple Tunnel
 description: |
   A simple tunnel written in golang
 
 grade: stable
-confinement: strict # use 'strict' once you have the right plugs and slots
+confinement: strict
 
 apps:
   gost:
@@ -15,9 +15,8 @@ apps:
 parts:
   gost:
     source: .
-    # See 'snapcraft plugins'
     plugin: go
-    go-packages: [github.com/ginuerzh/gost/cmd/gost]
     go-importpath: github.com/ginuerzh/gost
+    after: [go]
   go:
     source-tag: go1.8.3