Pin Werkzeug to below 2.1.x

We can’t upgrade to Werkzeug 2.1.0 because the `BaseResponse` class
has been renamed. The old version of Flask we are using tries to import
`BaseResponse` causing an error.

    See https://github.com/pallets/werkzeug/issues/1963

requirements.in

@@ -8,7 +8,7 @@ Flask==1.1.2  # pyup: <2
 Flask-WTF==1.0.1
 wtforms==3.0.1
 Flask-Login==0.6.1
-werkzeug==2.1.2
+werkzeug==2.0.3  # Can’t be upgraded until we are using Flask >= 2
 jinja2==3.0.3  # Can’t be upgraded until we are using Flask >= 2
 
 blinker==1.4

requirements.txt

@@ -213,7 +213,7 @@ urllib3==1.26.5
     #   requests
 webencodings==0.5.1
     # via bleach
-werkzeug==2.1.2
+werkzeug==2.0.3
     # via
     #   -r requirements.in
     #   flask