Merge pull request #311 from j5awry/pin-flask-and-werkzeug

Flask and werkzeug recently hit 2.0.0 milestones. This caused some
breaking changes related to flask-restx. Until some upstream bugs are
fixed, and we're able to identify all breaking changes, pin to < 2.0.0
versions. contrib: j5awry review: ziirish

Author: j5awry

requirements/install.pip

@@ -1,8 +1,8 @@
 aniso8601==8.0.0; python_version < '3.5'
 aniso8601>=0.82; python_version >= '3.5'
 jsonschema
-Flask>=0.8
-werkzeug
+Flask>=0.8, <2.0.0
+werkzeug <2.0.0
 pytz
 six>=1.3.0
 enum34; python_version < '3.4'