Support for elm-format as a fixer has existed since Sept 2017, but it's not
easy to discover because the fixer was named `format`. This breaks the
convention of the other fixers that use the full name in the registry.
I've gone ahead and fixed this discrepancy, but I left the existing registry
entry in place. We should move people towards using `elm-format` as the fixer
name, but I'd hate to break existing setups.
