Fix a couple typos

Author: DimitriPapadopoulos

docs/contributing.rst

@@ -195,7 +195,7 @@ HTTPS. Its three purposes are to be:
    for publishing on any Python package index
 
 
-Currently, twine has two principle functions: uploading new packages
+Currently, twine has two principal functions: uploading new packages
 and registering new `projects`_ (``register`` is no longer supported
 on PyPI, and is in Twine for use with other package indexes).
 

twine/repository.py

@@ -246,5 +246,5 @@ def release_urls(self, packages: List[package_file.PackageFile]) -> Set[str]:
 
     def verify_package_integrity(self, package: package_file.PackageFile) -> None:
         # TODO(sigmavirus24): Add a way for users to download the package and
-        # check it's hash against what it has locally.
+        # check its hash against what it has locally.
         pass