Avoid hard coded interpreter path

`/usr/bin/bash` doesn’t necessarily exist. For improved portability, use
`/usr/bin/env` to detect `bash` in the current environment.

lch.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/bash
+#!/usr/bin/env bash
 
 rm dist/favicon.ico
 mv dist/favicon-lch.ico dist/favicon.ico