📝 update reference link order (#442)

Author: guan404ming

CONTRIBUTING.md

@@ -224,13 +224,13 @@ one of the development dependencies.
 [gitmoji]: https://gitmoji.dev/
 [lefthook]: https://lefthook.dev/
 [markdownlint]: https://github.com/DavidAnson/markdownlint/tree/main
+[mkdocs]: https://www.mkdocs.org/
 [mypy]: https://github.com/python/mypy
 [numpy-commit-style]: https://numpy.org/devdocs/dev/development_workflow.html#writing-the-commit-message
 [ruff]: https://docs.astral.sh/ruff/
 [stub-style]: https://typing.python.org/en/latest/guides/writing_stubs.html#style-guide
 [test-docs]: https://github.com/numpy/numtype/tree/main/test
 [tool-docs]: https://github.com/numpy/numtype/tree/main/tool
 [tox]: https://github.com/tox-dev/tox
-[MkDocs]: https://www.mkdocs.org/
 
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