Replace get-pixels with ndarray-pixels

[briandonahue]

Addresses #246. In looking into that issue, I found this comment on get-pixels. ndarray-pixels relies on sharp and has been more recently maintained.

I updated color-thief to use it instead of get-pixels and all tests are passing. Hope this helps somebody!

[maiconcarraro]

@lokesh plans to merge this? and is it possible to buy you a coffee or sponsor to keep this project healthy?

[nathanchase]

@briandonahue Is there a possibility of pushing https://github.com/briandonahue/color-thief to npm in the meantime?

[briandonahue]

@nathanchase I didn't end up using colorthief in production (yet). Held off on the planned feature. I'm pretty swamped and have not pushed any public NPM packages. Anyone who wants to take my fork and publish a package is welcome to, though.

[maiconcarraro]

I'm using https://github.com/pioug/colorsuite until I find a better replacement