update omnibus cookbook version in Berkshelf.lock

This is a Berkshelf 2.0+ compat fix to fix the following error:

    Berkshelf could not find compatible versions for cookbook 'omnibus':
      In Berksfile:
        omnibus (~> 1.0.2)

      In Berksfile.lock:
        omnibus (1.0.0)

    Try running `berks update omnibus, which will try to find  'omnibus' matching '~> 1.0.2'.