Fix typo in tag checkout
Fix typo in tag checkout

`git checkout tag/[tag_name]` should be `git checkout tags/[tag_name]`
thomasvl/swift-protobuf,thomasvl/swift-protobuf,apple/swift-protobuf,allevato/swift-protobuf,tbkka/swift-protobuf,tbkka/swift-protobuf,apple/swift-protobuf,tbkka/swift-protobuf,cburrows/swift-protobuf,apple/swift-protobuf,allevato/swift-protobuf,thomasvl/swift-protobuf,allevato/swift-protobuf,allevato/swift-protobuf,tbkka/swift-protobuf,thomasvl/swift-protobuf,apple/swift-protobuf,thomasvl/swift-protobuf,cburrows/swift-protobuf,thomasvl/swift-protobuf,tbkka/swift-protobuf,apple/swift-protobuf,allevato/swift-protobuf,cburrows/swift-protobuf,allevato/swift-protobuf,thomasvl/swift-protobuf,cburrows/swift-protobuf,cburrows/swift-protobuf,apple/swift-protobuf,cburrows/swift-protobuf,tbkka/swift-protobuf,tbkka/swift-protobuf,allevato/swift-protobuf,apple/swift-protobuf,cburrows/swift-protobuf