AP_DDS: Use python3 shebang

Signed-off-by: Ryan Friedman <ryanfriedman5410+github@gmail.com>

libraries/AP_DDS/gen_config_h.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 '''
  process a *.h.in file to produce a *.h file
 '''

libraries/AP_DDS/wscript

@@ -1,5 +1,5 @@
-#!/usr/bin/env python
-# encoding: utf-8
+#!/usr/bin/env python3
+
 
 import os