Update and improve RVM dependencies

- `gawk` is now required by RVM (on Debian-based platforms)
  (see
  https://github.com/wayneeseguin/rvm/commit/45a85047d7f45b42cfcd8dd15eb95c1cfed1fe62
  and
  https://github.com/wayneeseguin/rvm/commit/4baf7d90d35d278ab891781d3237e18cebd47b5a)
- `maven` is now required (instead of `ant`) to build JRuby head
- Explictly depends on `sqlite` cookbook

BTW: Remove outdated metadata.json (this file is not required by chef solo)
Merge pull request #232 from gildegoma/rvm-deps

Update and improve RVM dependencies