setup: upper bound for ``idna``
setup: upper bound for ``idna``

* Adds an upper bound version ``2.6`` for ``idna`` module until the next
  ``requests`` is released. More details are in the following commit
  https://github.com/requests/requests/commit/f4ddf00c364e4396e7d941f91a8817311dd79adc
  which support ``2.6`` version. (closes inveniosoftware/invenio-app-ils#33)

Signed-off-by: Harris Tzovanakis <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@drjova.com>

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