Update #! env for python3

qa/zcash/test-depends-sources-mirror.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 
 # This script tests that the package mirror at https://download.z.cash/depends-sources/
 # contains all of the packages required to build this version of Zcash.

qa/zcash/updatecheck.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # This script checks for updates to zcashd's dependencies.
 #

src/test/bitcoin-util-test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2014 BitPay, Inc.
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or https://www.opensource.org/licenses/mit-license.php .

src/test/buildenv.py.in

@@ -1,2 +1,2 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 exeext="@EXEEXT@"