Explicitly check golint build on Go 1.5 and Go 1.6.
diff --git a/.travis.yml b/.travis.yml
index e33be0b..970855e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,7 @@
 language: go
+go:
+  - 1.5
+  - 1.6
 
 install:
   - go get -t -v ./...