Replace missing translation for StudyGroup member

Author: MrSerth

app/views/study_groups/_form.html.slim

@@ -10,7 +10,7 @@
       thead
         tr
           th = Exercise.human_attribute_name('selection')
-          th = StudyGroup.human_attribute_name('member')
+          th = ExternalUser.human_attribute_name('name')
       = collection_check_boxes :study_group, :study_group_membership_ids, @members, :id, :id do |b|
         tr
           td = b.check_box class: 'form-check-input'

app/views/study_groups/show.html.slim

@@ -14,7 +14,7 @@ h2.mt-4 = StudyGroup.human_attribute_name('members')
   table.table class=(@study_group.users.present? ? 'sortable' : '')
     thead
       tr
-        th = StudyGroup.human_attribute_name('member')
+        th = ExternalUser.human_attribute_name('name')
     - @study_group.users.each do |user|
       tr
         td = link_to_if(policy(user).show?, user.displayname, user)