This used to work due to side effects.
`rake parallel:migrate` used to work very inconsistently and would only migrate
some of the databases.
This introduces the recommended change to db.yml so the correct database is
found based off TEST_ENV_NUMBER if for some reason we did not set it using
RAILS_DB
Also avoids a bunch of schema dumping which is not needed when migrating
parallel specs
DB number 1 is very odd cause for whatever reason parallel spec is not
setting it.
Overcommit uses prebuilt hooks and require global installation.
To avoid this issues replace it with Lefthook.
Lefthook will be installed with npm packages. New contributors
will have fully consistent git hooks.
