fix: docker-entrypoint.sh uses safe shebang

Shebangs should use /usr/bin/env to locate the interpreter. Setting a path directly to the interpreter itself tends to be brittle and prone to breaking.

docker-entrypoint.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -eo pipefail # exit on error, error on any fail in pipe (not just last cmd); add -x to print each cmd; see gist bash_strict_mode.md