Update comment about default constant

Patch by: Dave Takahashi <dtcello@gmail.com> (@dtakahas)
Signed-off-by: Akira Matsuda <ronnie@dio.jp>

closes #1151

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56674 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/uri/common.rb

@@ -74,7 +74,7 @@ module URI
     #   String to replaces in.
     # +unsafe+::
     #   Regexp that matches all symbols that must be replaced with codes.
-    #   By default uses <tt>REGEXP::UNSAFE</tt>.
+    #   By default uses <tt>UNSAFE</tt>.
     #   When this argument is a String, it represents a character set.
     #
     # == Description