Fixed linting step (#368)

.circleci/config.yml

@@ -19,12 +19,13 @@ jobs:
           name: Linting
           command: |
             go fmt ./...
-            git diff --exit-code
             go get -u golang.org/x/lint/golint
             golint -set_exit_status
-            # golint adds stuff to go.mod and go.sum that mess
-            # with git status --porcelain later
+            # go fmt and golint can alter go.mod and go.sum,
+            # this will cause the git diff to give false negative
+            # restore those files before proceeding
             git checkout go.mod go.sum
+            git diff --exit-code
       - run:
           name: Test
           command: go test -v -race ./...