Fix Xcode case

[Frizlab]

Describe your changes

This is a dummy case change for Xcode.
Note I verified a single file, there might be other files with an incorrect case.

Issue ticket number and link

N/A

Checklist before requesting a review

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• Add Copyright if it missed:
  - "Copyright (c) 2019-present Axmol Engine contributors (see AUTHORS.md)."

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  Optional:

  • I have checked readme and add important infos to this PR.
  • I have added/adapted some tests too.

For core/new feature PR

• I have checked readme and add important infos to this PR.
• I have added thorough tests.

Axmol 3.x ------------------------------------------------------------

For each 3.x PR

• Check the '#include "axmol.h"' and replace it with the needed headers.