binman: Move to use Python 3

Update this tool to use Python 3 to meet the 2020 deadline.

Unfortunately this introduces a test failure due to a problem in pylibfdt
on Python 3. I will investigate.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/binman.py b/tools/binman/binman.py
index 8bd5868..9e6fd72 100755
--- a/tools/binman/binman.py
+++ b/tools/binman/binman.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # SPDX-License-Identifier: GPL-2.0+
 
 # Copyright (c) 2016 Google, Inc