Pin Jinja2 to 2.11.3 (#67)

8fc27f4 pinned MarkupSafe to
1.1.1, which lead to this error on our buildbots that are using
Python 3.10 to run the lnt client:
error: MarkupSafe 1.1.1 is installed but MarkupSafe>=2.0 is required by {'Jinja2'}

Jinja2 2.11.3 is the last version that will work with that version of
MarkupSafe:
https://github.com/pallets/jinja/blob/2.11.3/setup.py

The 3.x series moved to >= 2.0.0:
https://github.com/pallets/jinja/blob/3.0.0rc1/setup.py

Author: DavidSpickett

setup.py

@@ -119,7 +119,7 @@
         "aniso8601==1.2.0",
         "Flask==0.12.2",
         "Flask-RESTful==0.3.4",
-        "Jinja2",
+        "Jinja2==2.11.3",
         "MarkupSafe==1.1.1",
         "SQLAlchemy==1.3.24",
         "Werkzeug==0.15.6",