Delete memberships when deleting associated groups.

app/models/group.rb

@@ -1,7 +1,7 @@
 # Groups organize the User.
 # A Member gets the roles from the Group
 class Group < ActiveRecord::Base
-  has_many :memberships
+  has_many :memberships, dependent: :destroy
   has_many :users, :through => :memberships
 
   validates :name, :presence => true, :length => {:in => 1..25}
@@ -37,5 +37,3 @@ class Group < ActiveRecord::Base
     end
   end
 end
-
-