Update Travis config to Go 1.4.3, 1.5.4 and 1.6.1

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 9e6d621..96d8489 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,8 @@
 language: go
 go:
-  - 1.3
-  - release
+  - 1.4.3
+  - 1.5.4
+  - 1.6.1
   - tip
 
 script: