Merge pull request #4471 from semaperepelitsa/enum_sum

Pass a symbol instead of a block in Enumerable#sum

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -59,7 +59,7 @@ module Enumerable
     if block_given?
       map(&block).sum(identity)
     else
-      inject { |sum, element| sum + element } || identity
+      inject(:+) || identity
     end
   end