Fix golint dependency issue

.travis.yml

@@ -4,7 +4,9 @@ go:
 env:
   - "PATH=/home/travis/gopath/bin:$PATH"
 before_install:
-  - go get github.com/golang/lint/golint
+  - mkdir -p $(GOPATH)/src/golang.org/x 
+  - git clone --depth=1 https://github.com/golang/lint.git $(GOPATH)/src/golang.org/x/lint
+  - go get -u golang.org/x/lint/golint
   - go get github.com/mattn/goveralls
 script:
   - go vet