Fixed python2 in settings.py

settings.py was erroneously using python2. Replaced with python3.

qubesmanager/settings.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python2
+#!/usr/bin/python3
 #
 # The Qubes OS Project, http://www.qubes-os.org
 #
@@ -44,6 +44,7 @@ from PyQt4 import QtCore, QtGui  # pylint: disable=import-error
 
 from . import ui_settingsdlg  #pylint: disable=no-name-in-module
 
+
 # pylint: disable=too-many-instance-attributes
 class VMSettingsWindow(ui_settingsdlg.Ui_SettingsDialog, QtGui.QDialog):
     tabs_indices = collections.OrderedDict((