[2.2.x] Refs #31682 -- Doc'd minimal sqlparse version in Django 2.2.

Support for sqlparse < 0.2.2 was broken in
40b0a58 because is_whitespace property
was added in sqlparse 0.2.2.

Backport of 4339f2a from master.

docs/releases/2.2.txt

@@ -331,7 +331,7 @@ change shouldn't have an impact on your tests unless you've customized
 ``sqlparse`` is required dependency
 -----------------------------------
 
-To simplify a few parts of Django's database handling, `sqlparse
+To simplify a few parts of Django's database handling, `sqlparse 0.2.2+
 <https://pypi.org/project/sqlparse/>`_ is now a required dependency. It's
 automatically installed along with Django.