Upgraded pyexcel-io from 0.5.14 to 0.5.16. This change causes Werkzeug
to be upgraded from 0.14.1 to 0.15.1 which requires some changes:
* ProxyFix now needs to be imported from a different location
* The status code of RequestRedirect has changed from 301 to 308. Since
status code 308 is not currently supported on Internet Explorer with
Windows 7 and 8.1, this subclasses RequestRedirect to keep the status
code of 301.
changelog: https://werkzeug.palletsprojects.com/en/0.15.x/changes/#version-0-15-0