add a hard require to the ssh mixin

added hard require for SSHFactory into the ssh exploit mixin
this should prevent any laod-order bugs from cropping up again

lib/msf/core/exploit/ssh.rb

@@ -1,5 +1,6 @@
 module Msf
   module Exploit::Remote::SSH
+    require 'rex/socket/ssh_factory'
     def ssh_socket_factory
       Rex::Socket::SSHFactory.new(framework, self, datastore['Proxies'])
     end