Add image frame to gif about gif-encoder

[twolfson]

I'm going to guess you're using gif-stream for GIFDecoder:

https://www.npmjs.com/package/gif-stream

This package returns an array of RGB pixels whereas we expect RGBA. As a result, we are likely reading the second frame's red channel as our alpha channel.

I suggest attacking this in 2 parts:

• Get a script running locally with known RGBA data
  • Copy our checkerboard-pixels.json and verify it looks good
    • https://github.com/twolfson/gif-encoder/blob/0.6.0/test/test-files/checkerboard-pixels.json
  • Example usage: https://github.com/twolfson/gif-encoder/blob/0.6.0/test/gif-encoder_test.js#L9-L26
• Adjust gif-stream data to include alpha channel or move to a library that loads GIF frames with an alpha channel (e.g. get-pixels)
  • https://github.com/scijs/get-pixels