replace client.sys.config.getenv with get_env

Author: lilou1337

modules/exploits/windows/local/lenovo_systemupdate.rb

@@ -149,7 +149,7 @@ def exploit
     if datastore['WritableDir'] and not datastore['WritableDir'].empty?
       temp_dir = datastore['WritableDir']
     else
-      temp_dir = client.sys.config.getenv('TEMP')
+      temp_dir = get_env('TEMP')
     end
 
     print_status("Using #{temp_dir} to drop malicious exe")