snap: Revert build-snap to 1.11/stable channel for go

This is to fix the following snap build error:

    Failed to install or refresh a snap: 'go' does not exist
    or is not available on the desired channel '1.11.4/stable'.
    Use `snap info go` to get a list of channels the snap is available on.

`snap info go` reveals that the '1.11/stable' channel automatically
follows the latest minor point release as it becomes available.

snap/snapcraft.yaml

@@ -26,7 +26,7 @@ parts:
 
   hugo:
     plugin: nil
-    build-snaps: [go/1.11.4/stable]
+    build-snaps: [go/1.11/stable]
     source: .
     override-build: |
       set -ex