change concat by an alias

diff --git a/activesupport/lib/active_support/core_ext/string/output_safety.rb b/activesupport/lib/active_support/core_ext/string/output_safety.rb
index 3977971..567ba00 100644
--- a/activesupport/lib/active_support/core_ext/string/output_safety.rb
+++ b/activesupport/lib/active_support/core_ext/string/output_safety.rb
@@ -71,15 +71,12 @@ module ActiveSupport #:nodoc:
         super(ERB::Util.h(value))
       end
     end
+    alias << concat
 
     def +(other)
       dup.concat(other)
     end
 
-    def <<(value)
-      self.concat(value)
-    end
-
     def html_safe?
       true
     end
@@ -102,4 +99,4 @@ class String
   def html_safe
     ActiveSupport::SafeBuffer.new(self)
   end
-end
\ No newline at end of file
+end