installation: set minimum werkzeug version
installation: set minimum werkzeug version

* When running on Travis, the lower requirements build will
  end up installing werkzeug 0.15 together with Flask 0.11
  which are incompatible, to fix it, we set minimum requirement
  for werkzeug.

inveniosoftware/invenio-accounts,inveniosoftware/invenio-accounts,inspirehep/invenio-accounts,inveniosoftware/invenio-accounts,inspirehep/invenio-accounts,inspirehep/invenio-accounts