Update c-hashmap submodule

[Daaaav]

Changes:

• Hashmap keys are now const everywhere except in callbacks, meaning we don't need (char) and (void) casts whenever passing a const pointer anymore - so I cleaned up all these casts. (Guess C is a lot less strict with const than C++ is, and string literals aren't even const-qualified in C, but the reason hashmap keys aren't just const everywhere is because you may want to free a key based on a hashmap iteration).
• "no newline at end of file" warnings on macOS are fixed (for some reason, specifically macOS complained about that)
• "'return': conversion from 'uint64_t' to 'uint32_t', possible loss of data" warning on Windows is fixed (though Windows gives lots of these warnings, I guess /W4 is a bit too much...)

Legal Stuff:

By submitting this pull request, I confirm that...

• [x] My changes may be used in a future commercial release of VVVVVV
• [x] I will be credited in a CONTRIBUTORS file and the "GitHub Friends" section of the credits for all of said releases, but will NOT be compensated for these changes

[InfoTeddy]

• "no newline at end of file" warnings on macOS are fixed (for some reason, specifically macOS complained about that)

This is because of Clang's -Wnewline-eof, and macOS uses Clang by default.