docs: Fix to say "macos" instead of "mac" for the OS

See [1].

[1]: https://github.com/nexB/python-inspector/blob/a5891f4444f9ecbc4715b87b0f1b99f0e467ce71/etc/scripts/utils_thirdparty.py#L151

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>

Author: sschuberth

docs/source/dependencies-design.rst

@@ -198,7 +198,7 @@ selecting pre-built binary packages (options can be repeated):
 -  ``--python-version <python_version>``: the Python version(s) to use for
    wheels and dependency resolution. Can be repeated.
 -  ``--operating-system <os>`` : The OS(ses) to use for wheels: one of
-   linux, mac or windows. Can be repeated.
+   linux, macos or windows. Can be repeated.
 
 Notes: the assumption is that we only support X86/64 by default as an
 architecture for now. We could refine this later with support for