Use the default python3 version for nox in development (#694)

Co-authored-by: Pradyun Gedam <[email protected]>

Author: ananyo2012

noxfile.py

@@ -8,7 +8,7 @@
 nox.options.error_on_external_run = True
 
 
-@nox.session(python="3.5")
+@nox.session(python="3")
 def dev(session):
     session.install("-r", "requirements.txt")