When commit/rebase/push fails, reset to previous rev

[fredemmott]

e.g. if we have the commit:

  bottle do
+   :high_sierra
  done

but master now has:

  bottle do
    :mojave
  done

the patch will fail to apply, and git won't be able to merge it.

Instead:

1. throw away the commit adding the new bottle
2. update to latest master using rebase
3. use brew bottle --merge to re-create the commit on new base

This should stop #126 from re-occurring.