Rails5: Fix epics finder count_key method

In Rails5, the state enum value is passed instead of the
database integer.

ee/app/finders/epics_finder.rb

@@ -38,7 +38,11 @@ class EpicsFinder < IssuableFinder
   private
 
   def count_key(value)
-    Epic.states.invert[Array(value).last].to_sym
+    if Gitlab.rails5?
+      Array(value).last.to_sym
+    else
+      Epic.states.invert[Array(value).last].to_sym
+    end
   end
 
   # rubocop: disable CodeReuse/ActiveRecord

ee/changelogs/unreleased/rails5-epic-finder-fix.yml

+---
+title: 'Rails5: Fix epics finder count_key method In Rails5, the state enum value
+  is passed instead of the database integer.'
+merge_request: 7822
+author: Jasper Maes
+type: other