add tip to .travis.yml
diff --git a/.travis.yml b/.travis.yml
index 79780ec..73d5863 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,7 @@
 go:
   - 1.4
   - 1.5
+  - tip
 
 install:
   - go get -v ./...