One more fix to use Digest::MD5.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@1869 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/net/imap.rb

@@ -683,7 +683,7 @@ Struct
 
 require "socket"
 require "monitor"
-require "md5"
+require "digest/md5"
 
 module Net
   class IMAP