Test Go 1.9 (#31)

diff --git a/.travis.yml b/.travis.yml
index b6a6930..5895722 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,7 +5,7 @@
 go:
   - 1.7
   - 1.8
-  - tip
+  - 1.9
 
 cache:
   directories: