Source builds always build from valhalla master

[buildscientist]

Not sure if this intentional but when invoking

./build.sh source <version> the Docker build will always pull the valhalla repo from master due to how script/install_from_source.sh does a git clone and invokes the build process without switching to the version passed to the Docker build script.

Is the version passed supposed to correspond to the version of Valhalla from source that will be built - or is that solely a tag for the Docker image?