travis : use go1.7 to be future proof.

And, to reflect my own config `;-)`

.travis.yml

@@ -3,6 +3,7 @@ go:
   - 1.4.3
   - 1.5.3
   - 1.6
+  - 1.7
   - tip
 sudo: false
 before_install: 'git fetch --unshallow'
@@ -14,6 +15,7 @@ matrix:
     - go: tip
     - go: 1.4.3
     - go: 1.6
+    - go: 1.7
 notifications:
   irc:
     channels: