Remove deprecated (1.15) functions

[haljin]

warning: Exception.exception?/1 is deprecated. Use Kernel.is_exception/1 instead

starts to occur in Elixir 1.15. This should hopefully fix this, although it does require minimum Elixir version of 1.11 (https://hexdocs.pm/elixir/1.15.4/Kernel.html#is_exception/1) so I have updated mix.exs as well.

However that also means CI should be updated, but I am not sure how you'd prefer it? :)

[haljin]

Hi @expede is this repo still maintained at all?

[Valian]

Also looking forward to merging that PR, it's hard to use Exceptional with all these warnings.