Test Go 1.9 (#24)

diff --git a/.travis.yml b/.travis.yml
index 5ffa8fe..fc3936b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,7 @@
 go:
   - 1.7
   - 1.8
-  - tip
+  - 1.9
 
 cache:
   directories: