Fix a couple documentation typos. (GH-10498)

reproduciblity -> reproducibility
PyPA are the group -> PyPA is the group

Doc/installing/index.rst

@@ -48,7 +48,7 @@ Key terms
   repository of open source licensed packages made available for use by
   other Python users.
 * the `Python Packaging Authority
-  <https://www.pypa.io/>`__ are the group of
+  <https://www.pypa.io/>`__ is the group of
   developers and documentation authors responsible for the maintenance and
   evolution of the standard packaging tools and the associated metadata and
   file format standards. They maintain a variety of tools, documentation,

Doc/whatsnew/3.7.rst

@@ -432,7 +432,7 @@ and size) with source metadata saved in the cache file header when it was
 generated. While effective, this invalidation method has its drawbacks.  When
 filesystem timestamps are too coarse, Python can miss source updates, leading to
 user confusion. Additionally, having a timestamp in the cache file is
-problematic for `build reproduciblity <https://reproducible-builds.org/>`_ and
+problematic for `build reproducibility <https://reproducible-builds.org/>`_ and
 content-based build systems.
 
 :pep:`552` extends the pyc format to allow the hash of the source file to be