Update requirements because of broken package

Downgrade werkzeug and jsonschema, because their newest release break Flask and flask-restplus. More information --> pallets/flask#3486 and noirbizarre/flask-restplus#777

requirements.txt

@@ -2,4 +2,6 @@ Flask==1.0.2
 flask-jwt-extended==3.5.1
 flask-restplus==0.12.1
 requests==2.21.0
+werkzeug==0.16.1
+jsonschema==2.6.0
 git+https://github.com/qwc-services/qwc-services-core.git@b589e3dc3e20d221d59f7ee10226a46d1b60b9f9#egg=qwc-services-core