test: Add Python 2.7 to nox test environment

It is needed for sanity checking the code against the current
deployment environment.

Signed-off-by: Nabarun Pal <pal.nabarun95@gmail.com>

Author: palnabarun

noxfile.py

@@ -15,7 +15,7 @@ def dev(session):
     session.run("python", "manage.py", *session.posargs)
 
 
-@nox.session(python=["3.5", "3.6", "3.7", "3.8"])
+@nox.session(python=["2.7", "3.5", "3.6", "3.7", "3.8"])
 def test(session):
     session.install("-r", "requirements.txt")
     session.install("-r", "tools/requirements-test.txt")