Put missing nessus_scanner_list command back where it's supposed to be.

Must have deleted the line by accident somehow.

Author: SJCaldwell

plugins/nessus.rb

@@ -76,6 +76,7 @@ def commands
           "nessus_db_import" => "Import Nessus scan to the Metasploit connected database",
           "nessus_save" => "Save credentials of the logged in user to nessus.yml",
           "nessus_folder_list" => "List folders configured on the Nessus server",
+          "nessus_scanner_list" => "List the configured scanners on the Nessus server",
           "nessus_family_list" => "List all the plugin families along with their corresponding family IDs and plugin count"
         }
       end
@@ -1840,4 +1841,4 @@ def cleanup
       remove_console_dispatcher('Nessus')
     end
   end
-end
+end