Update stripe from 2.21.0 to 2.22.0

Author: pyup-bot

requirements/pip.txt

@@ -67,7 +67,7 @@ pytz==2018.9
 Unipath==1.1
 django-kombu==0.9.4
 mock==2.0.0
-stripe==2.21.0
+stripe==2.22.0
 
 # unicode-slugify==0.1.5 is not released on PyPI yet
 git+https://github.com/mozilla/unicode-slugify@b696c37#egg=unicode-slugify