Add description attribute to group API (GET and POST)

lib/api/entities.rb

@@ -65,7 +65,7 @@ module API
     end
 
     class Group < Grape::Entity
-      expose :id, :name, :path, :owner_id
+      expose :id, :name, :path, :owner_id, :description
     end
 
     class GroupDetail < Group

lib/api/groups.rb

@@ -47,7 +47,7 @@ module API
         authenticated_as_admin!
         required_attributes! [:name, :path]
 
-        attrs = attributes_for_keys [:name, :path]
+        attrs = attributes_for_keys [:name, :path, :description]
         @group = Group.new(attrs)
         @group.owner = current_user