Unneeded dependency on urllib3.
Unneeded dependency on urllib3.

Fixes issue infoportugal/wagtail-embedvideos#21.

SalahAdDin/wagtail-embedvideos,infoportugal/wagtail-embedvideos,SalahAdDin/wagtail-embedvideos,SalahAdDin/wagtail-embedvideos,infoportugal/wagtail-embedvideos,infoportugal/wagtail-embedvideos