fix(pypi): add python requests changelog URL (#2933)

add requests changelog

lib/datasource/index.js

@@ -45,6 +45,8 @@ const manualChangelogUrls = {
       'https://django-debug-toolbar.readthedocs.io/en/latest/changes.html',
     'firebase-admin':
       'https://firebase.google.com/support/release-notes/admin/python',
+    requests:
+      'http://docs.python-requests.org/en/master/community/updates/#release-and-version-history',
   },
 };