Remove gotestsum from the readme

It is not used any more

README.md

@@ -11,7 +11,6 @@ If you don't have or want to use Docker for building you need to make sure you h
 * go 1.14
 * `go get github.com/golang/protobuf/[email protected]`
 * `go get golang.org/x/tools/cmd/goimports`
-* `go get gotest.tools/[email protected]`
 * `go get github.com/golangci/golangci-lint/cmd/[email protected]`
 
 And then you can call the same make targets but you need to pass it the `builder.Makefile` (`make -f builder.Makefile`).