Add go 1.5 to tested versions

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 83e84ad..eeaf72b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,10 +2,10 @@
 script: "./test.sh"
 sudo: false
 go:
-    - 1.1
     - 1.2
     - 1.3
     - 1.4.1
+    - 1.5
     - tip
 before_install:
   - go get github.com/axw/gocov/gocov