Merge pull request #3832 from arunagw/indentation

indentation fix warning

activerecord/lib/active_record/relation.rb

@@ -154,7 +154,7 @@ def respond_to?(method, include_private = false)
     #
     # Please see further details in the
     # {Active Record Query Interface guide}[http://edgeguides.rubyonrails.org/active_record_querying.html#running-explain].
-   def explain
+    def explain
       _, sqls, binds = collecting_sqls_for_explain { exec_query }
       exec_explain(sqls, binds)
     end