[DOC] Fix links of cve [ci skip]

`http://www.cve.mitre.org/` seem to move `http://cve.mitre.org/`.
I can't access `http://www.cve.mitre.org/`.

[Fix GH-1857]

From: willnet <netwillnet@gmail.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63166 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/fileutils.rb

@@ -656,8 +656,8 @@ module FileUtils
   #
   # For details of this security vulnerability, see Perl's case:
   #
-  # * http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0448
-  # * http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0452
+  # * https://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0448
+  # * https://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0452
   #
   # For fileutils.rb, this vulnerability is reported in [ruby-dev:26100].
   #