update linux example persistence

Author: h00die

modules/exploits/example_linux_persistence.rb

@@ -56,7 +56,7 @@ def initialize(info = {})
         # What types of sessions we can use this module in conjunction with.  Most modules use libraries
         # which work on shell and meterpreter, but there may be a nuance between one of them, so best to
         # test both to ensure compatibility.
-        'SessionTypes' => [ 'shell', 'meterpreter' ],
+        'SessionTypes' => [ 'meterpreter' ], # @clean_up_rc only works in meterpreter sessions
         'Targets' => [[ 'Auto', {} ]],
         # from lib/msf/core/module/privileged, denotes if this requires or gives privileged access
         # since privilege escalation modules typically result in elevated privileges, this is