DeepMerge.deep_merge/3 has invalid spec

[thomas9911]

The spec says that the third argument should be a function with arity two but the examples and in the code a function with arity 3 is used.

current:

@spec deep_merge(map() | keyword(), map() | keyword(), (any(), any() -> any())) :: map() | keyword()

expected:

@spec deep_merge(map() | keyword(), map() | keyword(), (any(), any(), any() -> any())) :: map() | keyword()

[dsnipe]

@PragTob Hey, you made a very useful library, but this dialyzer error just doesn't allow me to use it in my project (CI uses dilyzer, so there must be no errors) Any update on this? I can open a PR, if you are ok.