Update doc for jwt example to omit b2s() if pyjwt version >= 2.0.0

[skip ci] jwt.encode() changed return type in 2.0.0 from byte to string.

Author: rouilj

doc/rest.txt

@@ -1926,6 +1926,8 @@ only been tested with python3)::
             secret = self.db.config.WEB_JWT_SECRET
             myjwt = jwt.encode(claim, secret, algorithm='HS256')
 
+	    # if jwt.__version__ >= 2.0.0 jwt.encode() returns string
+	    # not byte. So do not use b2s() with newer versions of pyjwt.
             result = {"jwt": b2s(myjwt),
                      }