Revert "Rename App::GitGerrit to Git::Gerrit"

This reverts commit 83fbcd081f58df2e4605b56a8344e7f505afd488.

Conflicts:
	lib/App/GitGerrit.pm

The CPAN indexing problem that I was trying to solve with that commit
was solved in another way. So, I'm renaming the module back to
App::GitGerrit.
v0.020

  [Changes]

  - Rename Git::Gerrit back to App::GitGerrit. The CPAN indexing
    problem is solved and it had nothing to do with the module's name.