Bump django from 1.11.17 to 1.11.18
Bump django from 1.11.17 to 1.11.18

Bumps [django](https://www.djangoproject.com/) from 1.11.17 to 1.11.18.

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
annapowellsmith/openpresc,annapowellsmith/openpresc,annapowellsmith/openpresc,ebmdatalab/openprescribing,ebmdatalab/openprescribing,annapowellsmith/openpresc,ebmdatalab/openprescribing,ebmdatalab/openprescribing