Use python3 in shebang

bin/radicale

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # This file is part of Radicale Server - Calendar Server
 # Copyright © 2008 Nicolas Kandel

radicale.fcgi

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # This file is part of Radicale Server - Calendar Server
 # Copyright © 2011-2016 Guillaume Ayoub

radicale.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # This file is part of Radicale Server - Calendar Server
 # Copyright © 2008 Nicolas Kandel

radicale.wsgi

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # This file is part of Radicale Server - Calendar Server
 # Copyright © 2011-2016 Guillaume Ayoub