make: Clearly specify python version for cmake_transform.

This makes sure that we always use python3 to run the
script, which is only supported on python3.

Change-Id: I0d0e42f368d2d26237bb467e692bee1bb56fd176
diff --git a/cmake_transform.py b/cmake_transform.py
index 0bac5a7..b93b1a0 100644
--- a/cmake_transform.py
+++ b/cmake_transform.py
@@ -1,4 +1,4 @@
-#!/bin/python
+#!/bin/python3
 import argparse
 import hashlib
 import json