Bump Travis versions (#370)

.travis.yml

@@ -4,15 +4,19 @@ services:
   - redis-server
 
 go:
-  - 1.4
   - 1.5.x
   - 1.6.x
   - 1.7.x
   - 1.8.x
   - 1.9.x
   - 1.10.x
+  - 1.11.x
   - tip
 
+matrix:
+  allow_failures:
+    - go: tip
+
 script:
   - go get -t -v ./...
   - diff -u <(echo -n) <(gofmt -d .)