Update .travis.yml

.travis.yml

@@ -1,6 +1,6 @@
 language: go
 go:
-- tip
+- 1.12.x
 gobuild_args: -x -ldflags "-X main.buildversion=$(git rev-parse HEAD)"
 before_install:
 - sudo apt-get install gcc-mingw-w64 gcc-mingw-w64-i686 gcc-mingw-w64-x86-64 binutils-mingw-w64-i686