remove deprecated werkzeug.cached_property

[kshefchek]

When booting biolink it exits at start-up with the exception:

  File "/opt/biolink-api/biolink/app.py", line 13, in <module>
    from biolink.api.restplus import api
  File "/opt/biolink-api/biolink/api/restplus.py", line 4, in <module>
    from flask_restplus import Api
  File "/opt/biolink-api/venv/lib/python3.6/site-packages/flask_restplus/__init__.py", line 4, in <module>
    from . import fields, reqparse, apidoc, inputs, cors
  File "/opt/biolink-api/venv/lib/python3.6/site-packages/flask_restplus/fields.py", line 17, in <module>
    from werkzeug import cached_property
ImportError: cannot import name 'cached_property'

See jarus/flask-testing#143

temporarily fixed by anchoring Werkzeug to 0.16.1

[kshefchek]

theres a large reduction in logs after changing werkzeug 0.16.1 (or perhaps from another dep being upgraded)