edit PyPi to PyPI in CONTRIBUTING.rst file

Co-authored-by: Matt Cieslak <[email protected]>

Author: gabridele

CONTRIBUTING.rst

@@ -103,7 +103,7 @@ Before you submit a pull request, check that it meets these guidelines:
 2.  If the pull request adds functionality, the docs should be updated. Put
     your new functionality into a function with a docstring, and add the
     feature to the list in README.rst.
-3.  The pull request should work for Python 3.9, 3.10, 3.11, 3.12 and 3.13, and for PyPi.
+3.  The pull request should work for Python 3.9, 3.10, 3.11, 3.12 and 3.13, and for PyPI.
     Check https://circleci.com/gh/PennLINC/CuBIDS
     and make sure that the tests pass for all supported Python versions.