bug: APISIX start error

[longshang]

Issue description

[emerg] 1#1: invalid number of arguments in "worker_shutdown_timeout" directive in /usr/local/apisix/conf/nginx.conf:21

Environment

• apisix version (cmd: apisix version):1.5
• OS: centos

Minimal test code / Steps to reproduce the issue

What's the actual result? (including assertion message & call stack if applicable)

What's the expected result?

[membphis]

please update your conf/config.yaml to latest version.

[moonming]

@longshang
Please use English in the public channel, thx