Run tests for 1.6

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index f08128c..8a6eebc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,9 +1,9 @@
 language: go
 script: "./test.sh"
 go:
-    - 1.3.3
     - 1.4.2
     - 1.5.3
+    - 1.6
     - tip
 before_install:
   - go get github.com/axw/gocov/gocov