Set python version explicitly to `2` to avoid issues on systems where

the default python version is `3`

Signed-off-by: Anagh Kumar Baranwal <anaghk.dos@gmail.com>

bin/make_backend_docs.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 """
 Make backend documentation
 """

bin/make_manual.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 """
 Make single page versions of the documentation for release and
 conversion into man pages etc.