Update Django and requests

[jwalgran]

Connects https://github.com/OpenTreeMap/otm-cloud/issues/457

Django release notes: https://docs.djangoproject.com/en/2.1/releases/1.11.5/ https://docs.djangoproject.com/en/2.1/releases/1.11.6/ https://docs.djangoproject.com/en/2.1/releases/1.11.7/ https://docs.djangoproject.com/en/2.1/releases/1.11.8/ https://docs.djangoproject.com/en/2.1/releases/1.11.9/ https://docs.djangoproject.com/en/2.1/releases/1.11.10/ https://docs.djangoproject.com/en/2.1/releases/1.11.11/ https://docs.djangoproject.com/en/2.1/releases/1.11.12/ https://docs.djangoproject.com/en/2.1/releases/1.11.13/ https://docs.djangoproject.com/en/2.1/releases/1.11.14/ https://docs.djangoproject.com/en/2.1/releases/1.11.15/ https://docs.djangoproject.com/en/2.1/releases/1.11.16/

requests release notes: http://docs.python-requests.org/en/master/community/updates/

The release notes for both libraries do not list any updates that I would expect to have a negative effect on OTM functionality.

[coveralls]

Coverage remained the same at 83.796% when pulling 975332e1bbdbf0e1476da32eccca31ac9c8c047d on jcw/dependency-updates into 0139ea1eb15936070838afad011091827c6f0a39 on hotfix/2.21.4.

[jwalgran]

Merging into the hotfix branch so that this can be deployed to staging and tested.