warning: character class has duplicated range

[dove-young]

I encountered 'character class has duplicated range' warning in ruby 2.0 environment.

->   ruby  -dvw -I~/Shell/GitHub/ruby-readability/lib -I~/Shell/GitHub/guess_html_encoding/lib test/read.rb 
ruby 2.0.0p353 (2013-11-22 revision 43784) [x86_64-linux]
~/Shell/GitHub/guess_html_encoding/lib/guess_html_encoding.rb:14: warning: character class has duplicated range: /charset=([\w\d-]+);?/
~/Shell/GitHub/guess_html_encoding/lib/guess_html_encoding.rb:22: warning: character class has duplicated range: /charset=([\w\d-]+);?/
~/Shell/GitHub/guess_html_encoding/lib/guess_html_encoding.rb:24: warning: character class has duplicated range: /<meta\s+charset=["']([\w\d-]+)?/

Seems removing \d from regexp would recover it. Below is a diff from git

->   git diff
diff --git a/lib/guess_html_encoding.rb b/lib/guess_html_encoding.rb
index 2ac074f..c39d973 100644
--- a/lib/guess_html_encoding.rb
+++ b/lib/guess_html_encoding.rb
@@ -11,7 +11,7 @@ module GuessHtmlEncoding
       headers = headers.map {|k, v| "#{k}: #{v}" }.join("\n") if headers.is_a?(Hash)
       headers = headers.dup.force_encoding("ASCII-8BIT")
       headers.split("\n").map {|i| i.split(":")}.each do |k,v|
-        if k =~ /Content-Type/i && v =~ /charset=([\w\d-]+);?/i
+        if k =~ /Content-Type/i && v =~ /charset=([\w-]+);?/i
           out = $1.upcase
           break
         end
@@ -19,9 +19,9 @@ module GuessHtmlEncoding
     end

     if out.nil? || out.empty? || !encoding_loaded?(out)
-      if html =~ /<meta[^>]*HTTP-EQUIV=["']?Content-Type["']?[^>]*content=["']([^'"]*)["']/i && $1 =~ /charset=([\w\d-]+);?/i
+      if html =~ /<meta[^>]*HTTP-EQUIV=["']?Content-Type["']?[^>]*content=["']([^'"]*)["']/i && $1 =~ /charset=([\w-]+);?/i
         out = $1
-      elsif html =~ /<meta\s+charset=["']([\w\d-]+)?/i
+      elsif html =~ /<meta\s+charset=["']([\w-]+)?/i
         out = $1
       end
       out.upcase! unless out.nil?