3 slashes works around an npm bug

asottile · asottile · commit 6088b1f9953c · 2019-02-17T12:17:46.000-08:00
https://npm.community/t/npm-install-g-git-file-c-path-to-repository-does-not-work-on-windows/5453
diff --git a/pre_commit/languages/node.py b/pre_commit/languages/node.py
@@ -62,7 +62,7 @@ def install_environment(prefix, version, additional_dependencies):
             cmd.extend(['-n', version])
         cmd_output(*cmd)
 
-        dep = 'git+file://{}'.format(prefix.prefix_dir)
+        dep = 'git+file:///{}'.format(prefix.prefix_dir)
         with in_env(prefix, version):
             helpers.run_setup_cmd(
                 prefix,
