Fixed typo in New-GitHubRepositoryFork for USAGE.md

Fix typo in USAGE.md

None.

[ ] You actually ran the code that you just wrote, especially if you did just "one last quick change".
[ ] Comment-based help added/updated, including examples.
[ ] Static analysis is reporting back clean.
[ ] New/changed code adheres to our coding guidelines.
[ ] Formatters were created for any new types being added.
[ ] New/changed code continues to support the pipeline.
[ ] Changes to the manifest file follow the manifest guidance.
[ ] Unit tests were added/updated and are all passing. See testing guidelines. This includes making sure that all pipeline input variations have been covered.
[ ] Relevant usage examples have been added/updated in USAGE.md.
[ ] If desired, ensure your name is added to our Contributors list

microsoft / PowerShellForGitHub