Fixed linting related dependency versions.

requirements.txt

@@ -81,7 +81,7 @@ unidecode
 python-json-logger
 recommonmark
 jinja2
-rdflib
+rdflib==5.0.0
 fastapi
 uvicorn[standard]
 a2wsgi==1.4.0
@@ -95,6 +95,8 @@ sphinx-click
 sphinx_rtd_theme
 gitpython
 mypy==0.730
+typed-ast==1.4.2
+astroid==2.5.1
 pylint==2.3.1
 pylint_plugin_utils==0.5
 pylint_mongoengine==0.3.3