Swift Protobuf breaking changes

[anjmao]

Hi,

I'm using Docker to build swift grpc protoc plugins. Recently apple released new swift-protobuf 1.1.1 version which is breaking grpc-swift.

This is my docker file

FROM swift:latest as swift_builder
RUN git clone https://github.com/grpc/grpc-swift \
    && cd grpc-swift \
    && make \
    && cp protoc-gen-swift protoc-gen-swiftgrpc /usr/bin/ \
    && cd / \
    && rm -rf grpc-swift

From logs I see that it resolves

Cloning https://github.com/apple/swift-protobuf.git
Resolving https://github.com/apple/swift-protobuf.git at 1.1.1

Compile Swift Module 'SwiftProtobuf' (76 sources)
Compile Swift Module 'Commander' (9 sources)
Compile Swift Module 'RootsEncoder' (1 sources)
Linking ./.build/x86_64-unknown-linux/debug/RootsEncoder
Compile Swift Module 'SwiftProtobufPluginLibrary' (18 sources)
Compile Swift Module 'SwiftGRPC' (32 sources)
Compile Swift Module 'Simple' (1 sources)
Compile Swift Module 'Echo' (4 sources)
Linking ./.build/x86_64-unknown-linux/debug/Simple
Linking ./.build/x86_64-unknown-linux/debug/Echo
Compile Swift Module 'protoc_gen_swift' (18 sources)
Linking ./.build/x86_64-unknown-linux/debug/protoc-gen-swift
Compile Swift Module 'protoc_gen_swiftgrpc' (9 sources)
Linking ./.build/x86_64-unknown-linux/debug/protoc-gen-swiftgrpc
Fetching https://github.com/apple/swift-protobuf.git
Fetching https://github.com/kylef/Commander.git
Fetching https://github.com/apple/swift-nio-zlib-support.git
Fetching https://github.com/apple/swift-nio-ssl-support.git
Fetching https://github.com/kylef/Spectre.git
Cloning https://github.com/apple/swift-protobuf.git
Resolving https://github.com/apple/swift-protobuf.git at 1.1.1

It looks like the problem is here https://github.com/grpc/grpc-swift/blob/master/Package.swift#L21. I could make a PR to lock versions.