[travis] Bump Go to 1.11

DirectXMan12 · DirectXMan12 · commit 029f9c8ed294 · 2018-11-12T10:47:32.000-08:00
This will match the version currently used in Kubernetes.
diff --git a/.travis.yml b/.travis.yml
@@ -5,7 +5,7 @@ os:
   - osx
 
 go:
-- "1.10"
+- "1.11.1"
 
 git:
   depth: 3
