使用 Laravel 框架创建一个样例后，部署到 Heroku，显示 500 server error

大家好，我是个新手。最近在学习Summer老师的《L01 Laravel 教程 - Web 开发实战入门 ( Laravel 6.x )》书。
做到第二章第4小节“部署上线”，一切正常，没有报错。但是代码push后，打开herokuapp网页，提示500 server error。我也删除过错误的，重新部署过新的项目，还是有此问题。
地址如下：
https://vast-bastion-41931.herokuapp.com/
下面是部分log：
vagrant@homestead:~/Code/weibo$ heroku logs
› Warning: heroku update available from 7.26.2 to 7.35.0.
2019-11-13T17:42:30.957961+00:00 app[api]: Enable Logplex by user berty0587@gmail.com
2019-11-13T17:42:30.957961+00:00 app[api]: Release v2 created by user berty0587@gmail.com
2019-11-13T17:42:30.856969+00:00 app[api]: Initial release by user berty0587@gmail.com
2019-11-13T17:42:30.856969+00:00 app[api]: Release v1 created by user berty0587@gmail.com
2019-11-13T17:43:55.816776+00:00 app[api]: Set APPKEY config vars by user berty0587@gmail.com
2019-11-13T17:43:55.816776+00:00 app[api]: Release v3 created by user berty0587@gmail.com
2019-11-13T17:44:06.000000+00:00 app[api]: Build started by user berty0587@gmail.com
2019-11-13T17:44:36.581963+00:00 app[api]: Deploy 55923969 by user berty0587@gmail.com
2019-11-13T17:44:36.581963+00:00 app[api]: Release v4 created by user berty0587@gmail.com
2019-11-13T17:44:36.601727+00:00 app[api]: Scaled to web@1:Free by user berty0587@gmail.com
2019-11-13T17:44:37.000000+00:00 app[api]: Build succeeded
2019-11-13T17:44:39.488107+00:00 heroku[web.1]: Starting process with command vendor/bin/heroku-php-apache2 public/
2019-11-13T17:44:42.661628+00:00 app[web.1]: DOCUMENTROOT changed to 'public/'
2019-11-13T17:44:42.719847+00:00 app[web.1]: Optimizing defaults for 1X dyno...
2019-11-13T17:44:42.757789+00:00 app[web.1]: 4 processes at 128MB memory limit.
2019-11-13T17:44:42.765219+00:00 app[web.1]: Starting php-fpm...
2019-11-13T17:44:44.768030+00:00 app[web.1]: Starting httpd...
2019-11-13T17:44:45.525401+00:00 heroku[web.1]: State changed from starting to up
2019-11-13T17:44:46.432727+00:00 app[web.1]: 10.150.246.196 - - [13/Nov/2019:17:44:46 +0000] "GET / HTTP/1.1" 500 1558 "https://dashboard.heroku.com/" "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.97 Safari/537.36
2019-11-13T17:44:46.618626+00:00 app[web.1]: 10.150.246.196 - - [13/Nov/2019:17:44:46 +0000] "GET /favicon.ico HTTP/1.1" 200 - "https://guarded-beyond-63670.herokuapp.com..." "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.97 Safari/537.36
2019-11-13T17:44:46.439642+00:00 heroku[router]: at=info method=GET path="/" host=guarded-beyond-63670.herokuapp.com requestid=fb47e598-0d52-4a7a-a3cc-5623637de93c fwd="208.89.50.34" dyno=web.1 connect=0ms service=241ms status=500 bytes=1782 protocol=https
2019-11-13T17:44:46.621653+00:00 heroku[router]: at=info method=GET path="/favicon.ico" host=guarded-beyond-63670.herokuapp.com requestid=3697e3ed-37c6-4fa3-ba0b-fb4839e8958a fwd="208.89.50.34" dyno=web.1 connect=1ms service=3ms status=200 bytes=231 protocol=https*

请高手们指点一二，小可不胜感激。