Update go dependencies

vendor/github.com/grpc-ecosystem/grpc-gateway/CONTRIBUTING.md

@@ -0,0 +1,35 @@
+# How to contribute
+
+Thank you for your contribution to grpc-gateway.
+Here's the recommended process of contribution.
+
+1. `go get github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway`
+2. `cd $GOPATH/src/github.com/grpc-ecosystem/grpc-gateway`
+3. hack, hack, hack...
+4. Make sure that your change follows best practices in Go
+   * [Effective Go](https://golang.org/doc/effective_go.html)
+   * [Go Code Review Comments](https://golang.org/wiki/CodeReviewComments)
+5. Make sure that `make test` passes. (use swagger-codegen 2.2.2, not newer versions)
+6. Sign [a Contributor License Agreement](https://cla.developers.google.com/clas)
+7. Open a pull request in Github
+
+When you work on a larger contribution, it is also recommended that you get in touch
+with us through the issue tracker.
+
+### Code reviews
+All submissions, including submissions by project members, require review.
+
+### I want to regenerate the files after making changes!
+
+Great, it should be as simple as thus (run from the root of the directory):
+
+```bash
+docker run -v $(pwd):/src/grpc-gateway --rm jfbrandhorst/grpc-gateway-build-env:1.12 \
+    /bin/bash -c 'cd /src/grpc-gateway && \
+        make realclean && \
+        make examples SWAGGER_CODEGEN="${SWAGGER_CODEGEN}"'
+docker run -itv $(pwd):/grpc-gateway -w /grpc-gateway --entrypoint /bin/bash --rm \
+    l.gcr.io/google/bazel -c 'bazel run :gazelle; bazel run :buildifier'
+```
+
+If this has resulted in some file changes in the repo, please ensure you check those in with your merge request.