Update source/hardware/controllers/pioneer_ddj_400.rst

Co-authored-by: ronso0 <ronso0@mixxx.org>

Author: daschuer

source/hardware/controllers/pioneer_ddj_400.rst

@@ -20,7 +20,7 @@ designed for rekordbox.
 
 - `Manufacturer's Product Page <https://www.pioneerdj.com/en/product/controller/ddj-400/black/overview/>`__
 - `Manufacturer's User Manual <https://support.alphatheta.com/articles/4404919716761?product=4416577146009>`__
-- `Manufacturer's Firmware Update <https://support.alphatheta.com/products/4416577146009?section=25/>`__
+- `Manufacturer's Firmware Update <https://support.alphatheta.com/products/4416577146009?section=25>`__
 - `Mapping Forum Thread <https://mixxx.discourse.group/t/pioneer-ddj-400/17476>`__
 
 .. versionadded:: 2.3.0