fix regexp introduced at recent RDoc update (r62924).

* lib/rdoc/text.rb: should escape `-` character.
  Sometimes test fails if `$VERBOSE = 1` with the following warning:

  > text.rb:172: warning: character class has duplicated range: ...


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62935 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rdoc/text.rb

@@ -169,7 +169,7 @@ module RDoc::Text
 
     encoding = text.encoding
 
-    text = text.gsub %r%Document-method:\s+[\w:.#=!?|^&<>~+-/*\%@`\[\]]+%, ''
+    text = text.gsub %r%Document-method:\s+[\w:.#=!?|^&<>~+\-/*\%@`\[\]]+%, ''
 
     space = ' '
     space = RDoc::Encoding.change_encoding space, encoding if encoding