Specify env python explicitly.

pre_commit/commands/install_uninstall.py

@@ -107,7 +107,7 @@ def install(
         before, rest = contents.split(TEMPLATE_START)
         to_template, after = rest.split(TEMPLATE_END)
 
-        before = before.replace('#!/usr/bin/env python', shebang())
+        before = before.replace('#!/usr/bin/env python3', shebang())
 
         hook_file.write(before + TEMPLATE_START)
         for line in to_template.splitlines():

pre_commit/resources/hook-tmpl

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """File generated by pre-commit: https://pre-commit.com"""
 from __future__ import print_function