Fix issue between flask-admin and werkzeug 1.0.0

Author: puckel

Dockerfile

@@ -59,6 +59,7 @@ RUN set -ex \
     && pip install pyOpenSSL \
     && pip install ndg-httpsclient \
     && pip install pyasn1 \
+    && pip install 'werkzeug<1.0.0' \
     && pip install apache-airflow[crypto,celery,postgres,hive,jdbc,mysql,ssh${AIRFLOW_DEPS:+,}${AIRFLOW_DEPS}]==${AIRFLOW_VERSION} \
     && pip install 'redis==3.2' \
     && if [ -n "${PYTHON_DEPS}" ]; then pip install ${PYTHON_DEPS}; fi \