Fix Ruby style

Author: wchen-r7

modules/auxiliary/admin/http/wp_symposium_sql_injection.rb

@@ -142,7 +142,7 @@ def run
       end
     end
 
-    if not credentials.empty?
+    unless credentials.empty?
       loot = store_loot("wp_symposium.http","text/plain", rhost, credentials)
       vprint_status("Credentials saved in: #{loot}")
     end