haskell-regex-tdfa: update overrides for ghc 8.4.1

The pull request we use does not suffice any longer because it does not update
the version constraint on base in the Cabal file.

Generally speaking, it might be a good idea to use
https://github.com/ChrisKuklewicz/regex-tdfa/pull/16 instead of the old one,
because it looks much cleaner. (It might have the same problem w/r to base,
though).

Pinging our resident GHC 8.4.1 guru @deepfire.