herokuにデプロイするとApplication Errorとなってしまう

達成したいこと

ruby on rails で作ったアプリをherokuにデプロイし、開くと
Application Errorとなってしまいます。
正常に開けるようにしたいです。

heroku logs

以下、heroku logsの内容です

2018-10-03T09:35:24.371279+00:00 app[api]: Release v1 created by user ihara.moeka@gmail.com
2018-10-03T09:35:24.371279+00:00 app[api]: Initial release by user ihara.moeka@gmail.com
2018-10-03T09:35:24.515088+00:00 app[api]: Release v2 created by user ihara.moeka@gmail.com
2018-10-03T09:35:24.515088+00:00 app[api]: Enable Logplex by user ihara.moeka@gmail.com
2018-10-03T09:36:26.000000+00:00 app[api]: Build started by user ihara.moeka@gmail.com
2018-10-03T09:37:17.000000+00:00 app[api]: Build failed -- check your build logs
2018-10-03T09:48:00.000000+00:00 app[api]: Build started by user ihara.moeka@gmail.com
2018-10-03T09:48:53.000000+00:00 app[api]: Build failed -- check your build logs

2018-10-03T10:01:32.000000+00:00 app[api]: Build started by user ihara.moeka@gmail.com
2018-10-03T10:02:26.000000+00:00 app[api]: Build failed -- check your build logs
2018-10-03T13:33:08.000000+00:00 app[api]: Build started by user ihara.moeka@gmail.com
2018-10-03T13:33:18.881145+00:00 app[api]: Release v3 created by user ihara.moeka@gmail.com
2018-10-03T13:33:18.909916+00:00 app[api]: Scaled to web@1:Free by user ihara.moeka@gmail.com
2018-10-03T13:33:18.881145+00:00 app[api]: Deploy 2eb678f1 by user ihara.moeka@gmail.com
2018-10-03T13:33:19.000000+00:00 app[api]: Build succeeded
2018-10-03T13:33:18.881145+00:00 app[api]: Deploy 2eb678f1 by user ihara.moeka@gmail.com
2018-10-03T13:33:19.000000+00:00 app[api]: Build succeeded
2018-10-03T13:33:22.217328+00:00 heroku[web.1]: Starting process with command `npm start`
2018-10-03T13:33:25.894599+00:00 heroku[web.1]: State changed from starting to crashed
2018-10-03T13:33:25.897278+00:00 heroku[web.1]: State changed from crashed to starting
2018-10-03T13:33:25.873871+00:00 heroku[web.1]: Process exited with status 1
2018-10-03T13:33:25.798264+00:00 app[web.1]: npm ERR! missing script: start
2018-10-03T13:33:25.808081+00:00 app[web.1]:
2018-10-03T13:33:25.808608+00:00 app[web.1]: npm ERR! A complete log of this run can be found in:
2018-10-03T13:33:25.808909+00:00 app[web.1]: npm ERR!     /app/.npm/_logs/2018-10-03T13_33_25_797Z-debug.log
2018-10-03T13:33:28.499182+00:00 heroku[web.1]: Starting process with command `npm start`
2018-10-03T13:33:32.930832+00:00 heroku[web.1]: State changed from starting to crashed
2018-10-03T13:33:32.916039+00:00 heroku[web.1]: Process exited with status 1
2018-10-03T13:33:32.831602+00:00 app[web.1]: npm ERR! missing script: start

2018-10-03T13:33:32.848673+00:00 app[web.1]:
2018-10-03T13:33:32.849134+00:00 app[web.1]: npm ERR! A complete log of this run can be found in:
2018-10-03T13:33:32.849474+00:00 app[web.1]: npm ERR!     /app/.npm/_logs/2018-10-03T13_33_32_833Z-debug.log
2018-10-03T13:33:35.278267+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=rocky-ocean-42853.herok
uapp.com request_id=d20cb4ac-0f79-4b90-bad8-bffbd88dcfd2 fwd="111.239.175.224" dyno= connect= service= status=503 bytes= protocol=http
s
2018-10-03T13:33:36.066209+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=rocky-ocean-
42853.herokuapp.com request_id=e384fabe-2e96-4a8f-b6ab-b3ee81868127 fwd="111.239.175.224" dyno= connect= service= status=503 bytes= pr
otocol=https