update Werkzeug to 0.15.5

Currently this setup doesn't work "out from the box" because of the compatibility bug in Werkzeug 0.15.3.
Bumping it to the 0.15.5 fixes the problem.
StackOverFlow issue: https://stackoverflow.com/questions/60140174/basic-flask-app-not-running-typeerror-required-field-type-ignores-missing-fr

Author: eadium

requirements.txt

@@ -20,5 +20,5 @@ SQLAlchemy==1.1.14
 sqlalchemy-migrate==0.11.0
 sqlparse==0.2.3
 Tempita==0.5.2
-Werkzeug==0.15.3
+Werkzeug==0.15.5
 WTForms==2.1