global: isort v4.3.4 and pytest v3.7.0
global: isort v4.3.4 and pytest v3.7.0

* Closes inveniosoftware/invenio#3940

Signed-off-by: Jan Okraska <57f2532bb355b938245ee70fb8b246c980a8dd1b@cern.ch>

inveniosoftware/invenio-previewer,inveniosoftware/invenio-previewer,inveniosoftware/invenio-previewer,inveniosoftware/invenio-previewer