drop 1.4 from travis

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 73d5863..3b26c7c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,5 @@
 language: go
 go:
-  - 1.4
   - 1.5
   - tip