travis: run tests on Go tip (#48)

Author: nathany

.travis.yml

@@ -2,7 +2,12 @@ sudo: false
 language: go
 
 go:
-   - 1.6.2
+  - 1.6.2
+  - tip
+
+matrix:
+  allow_failures:
+    - go: tip
 
 before_script:
   - go get -u github.com/golang/lint/golint