Update version to 1.3.1

BUILD

CMakeLists.txt

Makefile

build.yaml

gRPC-Core.podspec

gRPC-ProtoRPC.podspec

gRPC-RxLibrary.podspec

gRPC.podspec

package.json

package.xml

src/cpp/common/version_cc.cc

src/csharp/Grpc.Core/Version.csproj.include

src/csharp/Grpc.Core/VersionInfo.cs

src/csharp/build_packages_dotnetcli.bat

src/csharp/build_packages_dotnetcli.sh

src/node/health_check/package.json

src/node/tools/package.json

src/objective-c/!ProtoCompiler-gRPCPlugin.podspec

src/objective-c/GRPCClient/private/version.h

src/python/grpcio/grpc_version.py