Downgrading rdflib to ~=5.0" as RDFNamespace class is not available in rdflib~=6.0.

setup.py

@@ -6,15 +6,15 @@ with open("README.md", "r") as fh:
 setuptools.setup(
     name="jupyter-rdfify",
     version="1.0.2",
-    author="Lars Pieschel and Md. Rezaul Karim",
-    author_email="lars.pieschel@rwth-aachen.de/rezaul.karim@rwth-aachen.de",
+    author="Lars Pieschel & Md. Rezaul Karim",
+    author_email="lars.pieschel@rwth-aachen.de",
     description="IPython Extension for semantic web technology support (Turtle, SPARQL, ShEx, etc.)",
     long_description=long_description,
     long_description_content_type="text/markdown",
     url="https://git.rwth-aachen.de/i5/teaching/jupyter-rdfify",
     packages=setuptools.find_packages(),
     install_requires=[
-        "rdflib~=5.0",
+        "rdflib~=5.0"#_RDFNamespace class is not available in rdflib~=6.0. So, we need to downgrade it,
         "ipython>=7.0.0",
         "graphviz",
         "sparqlwrapper>=1.8.5",