Update .travis.yml

Author: vishr

.travis.yml

@@ -1,7 +1,7 @@
 language: go
 go:
-  - 1.7
-  - 1.8
+  - 1.7.x
+  - 1.8.x
   - tip
 install:
   - make dependency
@@ -11,4 +11,4 @@ after_success:
   - bash <(curl -s https://codecov.io/bash)
 matrix:
   allow_failures:
-    - go: tip
+    - go: tip