Fix install

http3.py

@@ -8,7 +8,7 @@ if isfile("../Procfile") and isfile("../requirements.txt"):
 if HEROKU:
     if not "aioquic" in open("../requirements.txt").read():
         print("Installing aioquic on this Heroku instance since it wasn't installed on deploy...")
-        system("pip install --user aioquic")
+        system("python3 -m pip install --user aioquic")
 
 import asyncio
 from typing import cast