Tor Browser 7.5 doesn't have a Browser/TorBrowser/Docs/sources/versions file

A user reported on the blog a problem using torbrowser-launcher: https://blog.torproject.org/comment/273588#comment-273588

It seems that torbrowser-launcher is looking at the file Browser/TorBrowser/Docs/sources/versions to find which version is installed, and fails if the file does not exists.

This file was present in the versions built with gitian/tor-browser-bundle, but is not in the versions built with rbm/tor-browser-build.