also include protoc-gen-go in tools, locking version during bootstrap

bootstrap.sh

@@ -22,7 +22,7 @@ then
   exit 1
 fi
 
+go mod download
+
 go get -u github.com/twitchtv/twirp/protoc-gen-twirp
 go get -u google.golang.org/protobuf/cmd/protoc-gen-go
-
-go mod download

tools/tools.go

@@ -5,4 +5,5 @@ package tools
 import (
 	_ "github.com/maxbrunsfeld/counterfeiter/v6"
 	_ "github.com/twitchtv/twirp/protoc-gen-twirp"
+	_ "google.golang.org/protobuf/cmd/protoc-gen-go"
 )