Update dockerfile and regenerate files

.circleci/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.13.1
+FROM golang:1.13.4
 
 # Warm apt cache and install dependencies
 # bzip2 is required by the node_tests (to extract its dependencies).
@@ -17,7 +17,7 @@ RUN echo -e '#!/bin/bash\njava -jar /usr/local/bin/swagger-codegen-cli.jar "$@"'
 	chmod +x /usr/local/bin/swagger-codegen
 
 # Install protoc
-ENV PROTOC_VERSION=3.9.2
+ENV PROTOC_VERSION=3.10.1
 RUN wget https://github.com/google/protobuf/releases/download/v${PROTOC_VERSION}/protoc-${PROTOC_VERSION}-linux-x86_64.zip \
     -O /protoc-${PROTOC_VERSION}-linux-x86_64.zip && \
     unzip /protoc-${PROTOC_VERSION}-linux-x86_64.zip -d /usr/local/ && \

.circleci/README.md

@@ -10,7 +10,7 @@ Great, it should be as simple as thus (run from the root of the directory):
 $ docker run -v $(pwd):/go/src/github.com/grpc-ecosystem/grpc-gateway --rm jfbrandhorst/grpc-gateway-build-env:1.13 \
     /bin/bash -c 'cd /go/src/github.com/grpc-ecosystem/grpc-gateway && \
         make realclean && \
-        make examples SWAGGER_CODEGEN="${SWAGGER_CODEGEN}"'
+        make examples'
 ```
 
 If this has resulted in some file changes in the repo, please ensure you check those in with your merge request.

CONTRIBUTING.md

@@ -27,7 +27,7 @@ Great, it should be as simple as thus (run from the root of the directory):
 docker run -v $(pwd):/src/grpc-gateway --rm jfbrandhorst/grpc-gateway-build-env:1.13 \
     /bin/bash -c 'cd /src/grpc-gateway && \
         make realclean && \
-        make examples SWAGGER_CODEGEN="${SWAGGER_CODEGEN}"'
+        make examples'
 docker run -itv $(pwd):/grpc-gateway -w /grpc-gateway --entrypoint /bin/bash --rm \
     l.gcr.io/google/bazel -c 'bazel run :gazelle -- update-repos -from_file=go.mod -to_macro=repositories.bzl%go_repositories; bazel run :buildifier'
 ```