update tb-manual build script
The former
GET_TB_VERSION="${tor_browser_bundle_dir}/gitian/get-tb-version"
is no longer valid and https://gitweb.torproject.org/tor-browser/user-manual.git/tree/configure.ac#n11 needs to be updated:
8.0
- TB_VERSION_ALPHA => https://gitweb.torproject.org/builders/tor-browser-build.git/tree/rbm.conf#n18
torbrowser_version: '8.5a1'
> locales:
> - ar
> ...
> - zh-TW
The version is currently not used, but the locales are needed by YELP.