Translate warn to warning for Elixir >= 1.11.0

[altjohndev]

Logger.compare_levels/2 triggers IO.warn/1 whenever we use it with :warn as parameter:

• https://github.com/elixir-lang/elixir/blob/v1.16.1/lib/logger/lib/logger.ex#L625-L630
• https://github.com/elixir-lang/elixir/blob/v1.16.1/lib/logger/lib/logger.ex#L1164-L1167

Sadly, any backend configured for Logger will translate :warning level to :warn for backward compatibility (ref), which makes the current implementation of this library to always trigger the IO warn message for warning logs.

This PR addresses that by converting the log :warn level to :warning before calling Logger.compare_levels/2 for Elixir >= 1.11.0.

[altjohndev]

Hi @AndrewDryga is this library currently active and accepting PRs?

[AndrewDryga]

Hello @altjohndev, sure we accept PR's. But I have a strong feeling that I want to rewrite this library as a logger formatter now :)

[andreyuhai]

Could we get a release with this PR, please? We have the same issue spamming us.
Until then we could use the commit hash. Turns out we can't, since our package depends on this package. :/

[AndrewDryga]

@andreyuhai @altjohndev sorry for making you wait guys, was trying to test it in our production first :). The version is published.