Fix compilation error with Elixir 1.14

[maltoe]

Since Elixir 1.14, the following results in a compilation error

defmodule Cocktail.Schedule do
  ...
  defimpl Inspect, for: __MODULE__ do
    ...
  end
end

Error looks like this:

==> cocktail
Compiling 21 files (.ex)

== Compilation error in file lib/cocktail/schedule.ex ==
** (CompileError) lib/cocktail/schedule.ex:251: cannot define module
Inspect.Kernel because it is currently being defined in
lib/cocktail/rule.ex:31
    lib/cocktail/schedule.ex:251: (module)

I checked the docs for a few Elixir versions back (at least 1.10), and they always said

When implementing a protocol for a struct, the :for option can be omitted if the defimpl call is inside the module that defines the struct

This patch removes the unnecessary for: __MODULE__ option to fix the compilation error.

---

Just FYI: It looks to me like a bug in Elixir 1.14, but I failed to reproduce it outside cocktail. It's not just the for: __MODULE__ by itself, at least. Unfortunately I don't really have the time to dig deeper right now. So if you could apply this patch, I'd be very grateful :)

[codecov[bot]]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (8c11308) compared to base (3dd3b6e). Patch has no changes to coverable lines.

Additional details and impacted files

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[vanvoljg]

This was short-lived issue that existed only in Elixir 1.14.0-1.14.1.

[maltoe]

@vanvoljg Not that it matters much, but you could have just merged the PR anyway, as it fixes the issue even for Elixir 1.14.0 and 1.14.1 :rocket: :grimacing: