Do not hardcode path to the Python interpreter

Use `/usr/bin/env python3` instead of `/usr/bin/python3` in the shebang
of Python scripts. This adds support for non-standard Python interpreter
paths such as the paths used in virtualenv environments.
Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

aurweb/git/auth.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import os
 import shlex

aurweb/git/serve.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import os
 import re

aurweb/git/update.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import os
 import pygit2

aurweb/scripts/aurblup.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import pyalpm
 import re

aurweb/scripts/mkpkglists.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import datetime
 import gzip

aurweb/scripts/notify.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import email.mime.text
 import subprocess

aurweb/scripts/pkgmaint.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import time
 

aurweb/scripts/popupdate.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import time
 

aurweb/scripts/rendercomment.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import re
 import pygit2

aurweb/scripts/tuvotereminder.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import subprocess
 import time

schema/gendummydata.py

-#!/usr/bin/python3
+#!/usr/bin/env python3
 """
 usage: gendummydata.py outputfilename.sql
 """