Update some of the docs links

Author: johanbrandhorst

docs/index.md

@@ -2,10 +2,10 @@
 
 [![CircleCI](https://circleci.com/gh/grpc-ecosystem/grpc-gateway.svg?style=svg)](https://circleci.com/gh/grpc-ecosystem/grpc-gateway)
 
-grpc-gateway is a plugin of [protoc](http://github.com/google/protobuf).
-It reads [gRPC](http://github.com/grpc/grpc-common) service definition,
+grpc-gateway is a plugin of [protoc](https://github.com/protocolbuffers/protobuf).
+It reads a [gRPC](https://grpc.io) service definition,
 and generates a reverse-proxy server which translates a RESTful JSON API into gRPC.
-This server is generated according to [custom options](https://cloud.google.com/service-management/reference/rpc/google.api#http) in your gRPC definition.
+This server is generated according to [custom options](https://cloud.google.com/service-infrastructure/docs/service-management/reference/rpc/google.api#http) in your gRPC definition.
 
 It helps you to provide your APIs in both gRPC and RESTful style at the same time.