Fixed issue with converting ArrayBuffer to base64

[vongrad]

There seems to be an issue with generating Epub with inline images using the following command:
percollate epub --inline https://da.m.wikipedia.org/wiki/Danmarks_historie

The function fetchBase64 does not properly convert the ArrayBuffer to base64 string and instead produces [object ArrayBuffer].
Example of the output:
<img data-file-height="355" data-file-width="330" decoding="async" src="data:image/png;base64,[object ArrayBuffer]" />

I have included a small patch that should fix this issue.

[danburzo]

Great catch, @vongrad! I carelessly replaced the buffer() deprecated call with arrayBuffer() and forgot about the serialization. Although not strictly necessary, could you please also import Buffer from node:buffer?

[vongrad]

Sure thing, it's imported now.

[danburzo]

Perfect, thank you for the fix!