fix help table

there was a bad class refernece here that
needed to be cleaned up

MS-1875

Author: David Maloney

lib/rex/ui/text/dispatcher_shell.rb

@@ -1,6 +1,7 @@
 # -*- coding: binary -*-
 require 'rex/ui'
 require 'pp'
+require 'rex/text/table'
 
 module Rex
 module Ui
@@ -201,7 +202,7 @@ def help_to_s(opts={})
       return "" if commands.nil? or commands.length == 0
 
       # Display the commands
-      tbl = Table.new(
+      tbl = Rex::Text::Table.new(
         'Header'  => "#{self.name} Commands",
         'Indent'  => opts['Indent'] || 4,
         'Columns' =>