fixed msfcli with missing require

msfcli was previously broken because of a missing require statement:
```
byt3bl33d3r@holeechit:/pentest/metasploit-framework$ ./msfcli 
/pentest/metasploit-framework/lib/rex/exploitation/powershell/script.rb:16:in `<class:Script>': uninitialized constant Rex::Exploitation::Powershell::Script::Forwardable (NameError)
	from /pentest/metasploit-framework/lib/rex/exploitation/powershell/script.rb:8:in `<module:Powershell>'
	from /pentest/metasploit-framework/lib/rex/exploitation/powershell/script.rb:7:in `<module:Exploitation>'
	from /pentest/metasploit-framework/lib/rex/exploitation/powershell/script.rb:6:in `<module:Rex>'
	from /pentest/metasploit-framework/lib/rex/exploitation/powershell/script.rb:5:in `<top (required)>'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /pentest/metasploit-framework/lib/rex/exploitation/powershell.rb:8:in `<top (required)>'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /pentest/metasploit-framework/lib/rex/text.rb:6:in `<top (required)>'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /pentest/metasploit-framework/lib/rex.rb:44:in `<top (required)>'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from ./msfcli:15:in `<main>'
```