Land rapid7#9292, fix variable name to store the username

Land rapid7#9292

Author: wchen-r7

modules/exploits/unix/webapp/wp_slideshowgallery_upload.rb

@@ -64,7 +64,7 @@ def exploit
       print_error("Unable to login as #{user}")
       return
     end
-    store_valid_credential(user: username, private: password, proof: cookie)
+    store_valid_credential(user: user, private: password, proof: cookie)
 
     print_status("Trying to upload payload")
     filename = "#{rand_text_alpha_lower(8)}.php"