Remove warning.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@27230 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rexml/parsers/baseparser.rb

@@ -31,7 +31,7 @@ module REXML
       COMBININGCHAR = '' # TODO
       EXTENDER = ''      # TODO
 
-      NCNAME_STR= "[#{LETTER}_:][-#{LETTER}#{DIGIT}._:#{COMBININGCHAR}#{EXTENDER}]*"
+      NCNAME_STR= "[#{LETTER}_:][-.\w:#{COMBININGCHAR}#{EXTENDER}]*"
       NAME_STR= "(?:(#{NCNAME_STR}):)?(#{NCNAME_STR})"
       UNAME_STR= "(?:#{NCNAME_STR}:)?#{NCNAME_STR}"