travis: enable go-{1.5,1.6,tip} and tests

.travis.yml

@@ -1,9 +1,17 @@
 language: go
 go:
   - 1.4
+  - 1.5.3
+  - 1.6
+  - tip
+
+matrix:
+  allow_failures:
+    - go: tip
 
 install:
  - go get golang.org/x/tools/cmd/cover
 
 script:
  - ./build-check
+ - ./test