adapter.rdf: Add trailing slash to AAS namespace

Previously, there was a trailing slash (`/`)
missing in the AAS namespace resulting in invalid
URIs, e.g.:

`https://admin-shell.io/aas/3/0Identifiable/`
instead of:
`https://admin-shell.io/aas/3/0/Identifiable/`.

This adds the trailing slash to the namespace in
the RDF serializer.

Fixes #365

basyx/aas/adapter/rdf/rdf_serialization.py

@@ -29,7 +29,7 @@
 from basyx.aas import model
 from .. import _generic
 
-NS_AAS = _generic.XML_NS_MAP["aas"]
+NS_AAS = _generic.XML_NS_MAP["aas"]+"/"
 
 
 class AASToRDFEncoder():