Crash when trying to export to PDF

When trying to export to PDF, for example the "Features" document, it crashes:

```
codimd_1 | 2022-08-09T15:29:54.388Z error: uncaughtException: Command failed: /home/hackmd/app/node_modules/phantomjs-prebuilt/lib/phantom/bin/phantomjs /home/hackmd/app/node_modules/markdown-pdf/ph
antom/render.js /tmp/tmp-23T217YkHOtWhW.html /tmp/tmp-238Mg00jNGpimx.pdf /home/hackmd/app /home/hackmd/app/node_modules/markdown-pdf/runnings.js /home/hackmd/app/node_modules/markdown-pdf/css/pdf.css /ho
me/hackmd/app/node_modules/highlight.js/styles/github-gist.css A4 portrait 2cm 0 10000
codimd_1 | This application failed to start because it could not find or load the Qt platform plugin "offscreen".
codimd_1 |
codimd_1 | Available platform plugins are: phantom.
codimd_1 |
codimd_1 | Reinstalling the application may fix this problem.
codimd_1 | PhantomJS has crashed. Please read the bug reporting guide at
codimd_1 | and file a bug report.
codimd_1 |
codimd_1 | Error: Command failed: /home/hackmd/app/node_modules/phantomjs-prebuilt/lib/phantom/bin/phantomjs /home/hackmd/app/node_modules/markdown-pdf/phantom/render.js /tmp/tmp-23T217YkHOtWhW.html /
tmp/tmp-238Mg00jNGpimx.pdf /home/hackmd/app /home/hackmd/app/node_modules/markdown-pdf/runnings.js /home/hackmd/app/node_modules/markdown-pdf/css/pdf.css /home/hackmd/app/node_modules/highlight.js/styles
/github-gist.css A4 portrait 2cm 0 10000
codimd_1 | This application failed to start because it could not find or load the Qt platform plugin "offscreen".
codimd_1 |
codimd_1 | Available platform plugins are: phantom.
codimd_1 |
codimd_1 | Reinstalling the application may fix this problem.
codimd_1 | PhantomJS has crashed. Please read the bug reporting guide at
codimd_1 | and file a bug report.
codimd_1 |
codimd_1 | at ChildProcess.exithandler (child_process.js:294:12)
codimd_1 | at ChildProcess.emit (events.js:198:13)
codimd_1 | at maybeClose (internal/child_process.js:982:16)
codimd_1 | at Process.ChildProcess._handle.onexit (internal/child_process.js:259:5)
codimd_1 | 2022-08-09T15:29:54.388Z error: An uncaught exception has occured.
codimd_1 | 2022-08-09T15:29:54.388Z error: Command failed: /home/hackmd/app/node_modules/phantomjs-prebuilt/lib/phantom/bin/phantomjs /home/hackmd/app/node_modules/markdown-pdf/phantom/render.js /tm
p/tmp-23T217YkHOtWhW.html /tmp/tmp-238Mg00jNGpimx.pdf /home/hackmd/app /home/hackmd/app/node_modules/markdown-pdf/runnings.js /home/hackmd/app/node_modules/markdown-pdf/css/pdf.css /home/hackmd/app/node_
modules/highlight.js/styles/github-gist.css A4 portrait 2cm 0 10000
codimd_1 | This application failed to start because it could not find or load the Qt platform plugin "offscreen".
codimd_1 |
codimd_1 | Available platform plugins are: phantom.
codimd_1 |
codimd_1 | Reinstalling the application may fix this problem.
codimd_1 | PhantomJS has crashed. Please read the bug reporting guide at
codimd_1 | and file a bug report.
codimd_1 |
codimd_1 | { Error: Command failed: /home/hackmd/app/node_modules/phantomjs-prebuilt/lib/phantom/bin/phantomjs /home/hackmd/app/node_modules/markdown-pdf/phantom/render.js /tmp/tmp-23T217YkHOtWhW.html /tmp/tmp-238Mg00jNGpimx.pdf /home/hackmd/app /home/hackmd/app/node_modules/markdown-pdf/runnings.js /home/hackmd/app/node_modules/markdown-pdf/css/pdf.css /home/hackmd/app/node_modules/highlight.js/styles/github-gist.css A4 portrait 2cm 0 10000
codimd_1 | This application failed to start because it could not find or load the Qt platform plugin "offscreen".
codimd_1 |
codimd_1 | Available platform plugins are: phantom.
codimd_1 |
codimd_1 | Reinstalling the application may fix this problem.
codimd_1 | PhantomJS has crashed. Please read the bug reporting guide at
codimd_1 | and file a bug report.
codimd_1 |
codimd_1 | at ChildProcess.exithandler (child_process.js:294:12)
codimd_1 | at ChildProcess.emit (events.js:198:13)
codimd_1 | at maybeClose (internal/child_process.js:982:16)
codimd_1 | at Process.ChildProcess._handle.onexit (internal/child_process.js:259:5)
codimd_1 | killed: false,
codimd_1 | code: null,
codimd_1 | signal: 'SIGABRT',
codimd_1 | cmd:
codimd_1 | '/home/hackmd/app/node_modules/phantomjs-prebuilt/lib/phantom/bin/phantomjs /home/hackmd/app/node_modules/markdown-pdf/phantom/render.js /tmp/tmp-23T217YkHOtWhW.html /tmp/tmp-238Mg00jNGpimx.pdf /home/hackmd/app /home/hackmd/app/node_modules/markdown-pdf/runnings.js /home/hackmd/app/node_modules/markdown-pdf/css/pdf.css /home/hackmd/app/node_modules/highlight.js/styles/github-gist.css A4 portrait 2cm 0 10000',
codimd_1 | level: 'error',
codimd_1 | timestamp: '2022-08-09T15:29:54.388Z',
codimd_1 | [Symbol(level)]: 'error',
codimd_1 | [Symbol(message)]:
codimd_1 | '2022-08-09T15:29:54.388Z error: \tCommand failed: /home/hackmd/app/node_modules/phantomjs-prebuilt/lib/phantom/bin/phantomjs /home/hackmd/app/node_modules/markdown-pdf/phantom/render.js /tmp/tmp-23T217YkHOtWhW.html /tmp/tmp-238Mg00jNGpimx.pdf /home/hackmd/app /home/hackmd/app/node_modules/markdown-pdf/runnings.js /home/hackmd/app/node_modules/markdown-pdf/css/pdf.css /home/hackmd/app/node_modules/highlight.js/styles/github-gist.css A4 portrait 2cm 0 10000\nThis application failed to start because it could not find or load the Qt platform plugin "offscreen".\n\nAvailable platform plugins are: phantom.\n\nReinstalling the application may fix this problem.\nPhantomJS has crashed. Please read the bug reporting guide at\n and file a bug report.\n' }
codimd_1 | 2022-08-09T15:29:54.391Z error: Process will exit now.
codimd_codimd_1 exited with code 1
```

I use the latest docker image, hackmdio/hackmd:2.4.2-cjk.

Thanks for your help.