Force werkzeug to a specific version to avoid failures

requirements.txt

@@ -13,4 +13,5 @@ Flask-Caching==1.8.0
 pylibmc==1.6.1
 Flask-Limiter==1.2.1
 psycopg2==2.8.5
-pymemcache==3.1.0
\ No newline at end of file
+pymemcache==3.1.0
+Werkzeug==1.0.1
\ No newline at end of file