Fix ruby's uri parser to adapt subdomains including underscores

diff

--- a/uri/common.rb
+++ b/uri/rfc3986_common.rb
@@ -45,9 +45,9 @@ module URI
       RESERVED = ";/?:@&=+$,\\[\\]"
 
       # domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
-      DOMLABEL = "(?:[#{ALNUM}](?:[-#{ALNUM}]*[#{ALNUM}])?)"
+      DOMLABEL = "(?:[#{ALNUM}](?:[-_#{ALNUM}]*[#{ALNUM}])?)"
       # toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
-      TOPLABEL = "(?:[#{ALPHA}](?:[-#{ALNUM}]*[#{ALNUM}])?)"
+      TOPLABEL = "(?:[#{ALPHA}](?:[-_#{ALNUM}]*[#{ALNUM}])?)"
       # hostname      = *( domainlabel "." ) toplabel [ "." ]
       HOSTNAME = "(?:#{DOMLABEL}\\.)*#{TOPLABEL}\\.?"
 
@@ -365,7 +365,7 @@ module URI
       # hostname      = *( domainlabel "." ) toplabel [ "." ]
       # reg-name      = *( unreserved / pct-encoded / sub-delims ) # RFC3986
       unless hostname
-        ret[:HOSTNAME] = hostname = "(?:[a-zA-Z0-9\\-.]|%\\h\\h)+"
+        ret[:HOSTNAME] = hostname = "(?:[a-zA-Z0-9\\-._]|%\\h\\h)+"
       end
 
       # RFC 2373, APPENDIX B: