communicator/ssh: bind variable value to closure

Fixes the following vet report:

communicator/ssh/communicator_test.go:88: range variable newChannel captured by func literal

communicator/ssh/communicator_test.go

@@ -83,10 +83,10 @@ func newMockLineServer(t *testing.T) string {
 			}
 			t.Log("Accepted channel")
 
-			go func() {
+			go func(channelType string) {
 				defer channel.Close()
-				conn.OpenChannel(newChannel.ChannelType(), nil)
+				conn.OpenChannel(channelType, nil)
-			}()
+			}(newChannel.ChannelType())
 		}
 		conn.Close()
 	}()