Fix access to SurveyAssignment custom_email
Fix access to SurveyAssignment custom_email

After Rails 5, the email saves with symbols as keys instead of strings.

feelfreelinux/WikiEduDashboard,majakomel/WikiEduDashboard,alpha721/WikiEduDashboard,sejalkhatri/WikiEduDashboard,majakomel/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,KarmaHater/WikiEduDashboard,Wowu/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,majakomel/WikiEduDashboard,feelfreelinux/WikiEduDashboard,feelfreelinux/WikiEduDashboard,sejalkhatri/WikiEduDashboard,KarmaHater/WikiEduDashboard,sejalkhatri/WikiEduDashboard,sejalkhatri/WikiEduDashboard,alpha721/WikiEduDashboard,alpha721/WikiEduDashboard,alpha721/WikiEduDashboard,sejalkhatri/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,feelfreelinux/WikiEduDashboard,KarmaHater/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,Wowu/WikiEduDashboard,Wowu/WikiEduDashboard,Wowu/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,majakomel/WikiEduDashboard,KarmaHater/WikiEduDashboard