[setup.py] Upgrade rdflib and dependencies

Remove the rdflib 5.0.0 pin and upgrade to the latest rdflib
distribution. Also upgrade dependent test library owlrl and
remove the pinned pyparsing version that rdflib 5.0.0 was
dependent on.

Author: mpsonntag

setup.py

@@ -31,13 +31,9 @@
 with open('README.md') as f:
     description_text = f.read()
 
-# pyparsing needs to be pinned to 2.4.7 for the time being. setup install fetches a pre-release
-# package that currently results in issues with the rdflib library.
-install_req = ["lxml", "pyyaml>=5.1", "rdflib==5.0.0", "docopt", "pathlib", "pyparsing==2.4.7"]
-
-# owlrl depends on rdflib - the pinned version should be removed once the version pin has also been
-# removed from rdflib. Also needs to be updated in requirements-test.txt
-tests_req = ["pytest", "owlrl==5.2.3", "requests"]
+install_req = ["docopt", "lxml", "pathlib", "pyyaml>=5.1", "rdflib>=6.0.0"]
+# owlrl depends on rdflib; update any changes in requirements-test.txt as well.
+tests_req = ["owlrl", "pytest", "requests"]
 
 setup(
     name='odML',