add go 1.12.x into travis.yml and appveyor.yml

.travis.yml

@@ -3,6 +3,7 @@ language: go
 go:
   - 1.10.x
   - 1.11.x
+  - 1.12.x
 
 branches: # build only on these branches
   only:

appveyor.yml

@@ -29,3 +29,4 @@ environment:
   matrix:
     - go: 1.10.x
     - go: 1.11.x
+    - go: 1.12.x