Upgrade Django from 1.8.17 to 1.8.18
Upgrade Django from 1.8.17 to 1.8.18

(cherry picked from commit 410133d8e8be6ece3c71dce526ee9fa5234b1616)

Stanford-Online/edx-platform,Edraak/edraak-platform,caesar2164/edx-platform,Edraak/edraak-platform,caesar2164/edx-platform,Edraak/edraak-platform,pabloborrego93/edx-platform,gymnasium/edx-platform,Stanford-Online/edx-platform,appsembler/edx-platform,gymnasium/edx-platform,Stanford-Online/edx-platform,appsembler/edx-platform,pabloborrego93/edx-platform,caesar2164/edx-platform,gymnasium/edx-platform,Edraak/edraak-platform,pabloborrego93/edx-platform,gymnasium/edx-platform,caesar2164/edx-platform,pabloborrego93/edx-platform,appsembler/edx-platform,appsembler/edx-platform,Stanford-Online/edx-platform