Update modules/exploits/multi/persistence/ssh_key.rb

Co-authored-by: jheysel-r7 <Jack_Heysel@rapid7.com>

Author: h00die

modules/exploits/multi/persistence/ssh_key.rb

@@ -35,7 +35,7 @@ def initialize(info = {})
           'h00die <mike@shorebreaksecurity.com>', # linux
           'Dean Welch <dean_welch[at]rapid7.com>' # windows
         ],
-        'Platform' => [], # this is used for payload selection but we don't use a payload
+        'Platform' => %w[linux unix win], # this must be defined despite the module not using a payload
         'Arch' => ARCH_ALL, # doesn't matter because we don't use the payload
         'SessionTypes' => [ 'meterpreter', 'shell' ],
         'References' => [