travis: check gofmt, capture errors from golint

golint does not exit with code!=0 on errors, so travis build
will continue with success, therefore using "test -z".

Adding gofmt check.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>

.travis.yml

@@ -11,9 +11,10 @@ before_install:
 
 script:
   - go vet -x ./...
-  - golint ./...
+  - test -z "$(golint ./...)"
+  - test -z "$(gofmt -s -l -w . | tee /dev/stderr)"
   - go test -v  ./...
   - go test -covermode=count -coverprofile=profile.cov
 
 after_script:
-  - goveralls -coverprofile=profile.cov -service=travis-ci
+  - goveralls -coverprofile=profile.cov -service=travis-ci