Making SafeBuffer << an alias for concat method

[#3848 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

activesupport/lib/active_support/core_ext/string/output_safety.rb

@@ -71,15 +71,12 @@ def concat(value)
         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 @@ def html_safe!
   def html_safe
     ActiveSupport::SafeBuffer.new(self)
   end
-end
\ No newline at end of file
+end