$wgGitRepositoryViewers to link to gitweb

$wgGitRepositoryViewers to link to gitweb

My git remote is configured just to be ssh://review/mediawiki/core.git
and I have "review" set up in $HOME/.ssh/config.

Unfortunately, I need to change git remote URLs to make sure
the repository is linked from Special:Version.

This shouldn't be necessary; either we should fallback to the
official MediaWiki git repository or we should add the configuration
option to adapt to local needs.

Change-Id: I2e0b6470c16ec36d0e94cceab844f4a4c4334067