travis: fix fetch issue of golint

As golint repo does not return metadata for "go get" to work correctly,
every travis build fails. Let's install golint without using go get
until it's fixed.

See also golang/lint#397

Signed-off-by: Dongsu Park <[email protected]>

Author: Dongsu Park

.travis.yml

@@ -7,7 +7,9 @@ go:
 sudo: false
 
 before_install:
-  - go get github.com/golang/lint/golint
+  - mkdir --parents $GOPATH/src/golang.org/x
+    && git clone --depth=1 https://go.googlesource.com/lint $GOPATH/src/golang.org/x/lint
+    && go get golang.org/x/lint/golint
   - go get github.com/vbatts/git-validation
 
 install: true