Timber.add_context wrong typespec

[gabrielpra1]

Timber.add_context has the typespec @spec add_context(map()) :: :ok, even though the function also accepts a keyword list as parameter.

This causes Dialyzer to throw misleading warnings:

The call 'Elixir.Timber':add_context([{'origin','tracker'},...]) will never return since the success typing is (map()) -> 'ok' and the contract is (map()) -> 'ok'