Catch first arg with shorten

lib/msf/core/exploit/powershell.rb

@@ -163,6 +163,9 @@ module Exploit::Powershell
 
     # Shorten arg if PSH 2.0+
     if opts[:shorten]
+      # Invoke-Command and Out-File require these options to have
+      # an additional space before to prevent Powershell code being
+      # mangled.
       arg_string.gsub!(' -Command ', ' -c ')
       arg_string.gsub!('-EncodedCommand ', ' -e ')
       arg_string.gsub!('-ExecutionPolicy ', ' -ep ')