imports_params_def_usertype_imported.ksy: add missing import

I forgot to add this import, but KSC didn't report it as an error due to
kaitai-io/kaitai_struct#534. I'm fixing it
because I don't want this test to stop working once
kaitai-io/kaitai_struct#534 is resolved.

formats/imports_params_def_usertype_imported.ksy

@@ -5,6 +5,7 @@
 meta:
   id: imports_params_def_usertype_imported
   imports:
+    - hello_world
     - params_def_usertype_imported
 seq:
   - id: hw