Add missing comment char to RDoc comment

This fixes incorrect rendering in the generated documentation.

on-behalf-of: @Cofense <oss@cofense.com>

activerecord/lib/active_record/relation/calculations.rb

@@ -31,7 +31,7 @@ module ActiveRecord
     #
     #   Article.group(:status, :category).count
     #   # =>  {["draft", "business"]=>10, ["draft", "technology"]=>4,
-    #          ["published", "business"]=>0, ["published", "technology"]=>2}
+    #   #      ["published", "business"]=>0, ["published", "technology"]=>2}
     #
     # If #count is used with {Relation#select}[rdoc-ref:QueryMethods#select], it will count the selected columns:
     #