Configure Travis to use Go1.7.

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 970855e..3865f0a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,7 @@
 language: go
 go:
-  - 1.5
   - 1.6
+  - 1.7
 
 install:
   - go get -t -v ./...