Add more golang versions for build

Author: chenrui333

.travis.yml

@@ -2,7 +2,11 @@ dist: bionic
 language: go
 
 go:
-  - "1.13"
+  - "1.9.x"
+  - "1.10.x"
+  - "1.11.x"
+  - "1.12.x"
+  - "1.13.x"
 
 branches:
   only:
@@ -11,7 +15,7 @@ branches:
 env:
   global:
     - GO111MODULE=on
-    - GOPROXY=https://goproxy.io
+    - GOPROXY=https://proxy.golang.org,direct
 
 install: make bootstrap