chore: add env for go1.11/go1.12

.travis.yml

@@ -13,6 +13,14 @@ go:
 git:
   depth: 10
 
+matrix:
+  fast_finish: true
+  include:
+  - go: 1.11.x
+    env: GO111MODULE=on
+  - go: 1.12.x
+    env: GO111MODULE=on
+
 script:
   - go test -v -covermode=count -coverprofile=coverage.out