Allow mtl-2.3

[LaurentRDC]

Hi,

mtl 2.3.1 has been released for about a month, and the latest version of relude is preventing me from updating.

Checklist:

HLint

• I've changed the exposed interface (add new reexports, remove reexports, rename reexported things, etc.).
  • I've updated hlint.dhall accordingly to my changes (add new rules for the new imports, remove old ones, when they are outdated, etc.).
  • I've generated the new .hlint.yaml file (see this instructions).

General

• I've updated the CHANGELOG with the short description of my latest changes.
• All new and existing tests pass.
• I keep the code style used in the files I've changed (see style-guide for more details).
• I've used the stylish-haskell file.
• My change requires the documentation updates.
  • I've updated the documentation accordingly.
• I've added the [ci skip] text to the docs-only related commit's name.

[vrom911]

Thanks a lot!
This was done in #433