travis: add 1.9.x instead 1.9 to go version (#1105)

1.9.x should be working now.

.travis.yml

@@ -4,7 +4,7 @@ go:
   - 1.6.x
   - 1.7.x
   - 1.8.x
-  - 1.9
+  - 1.9.x
   - master
 
 git: