Update get-pixels and save-pixels to fix vulnerability in jpeg-js

[rabin-outlier]

Currently gif-frames is using old and modified versions of get-pixels and save-pixels library.
The npm links to the libraries in package.json already point to their parent library.
Also, gif-frames is currently using a vulnerable version of jpeg-js as a dependency.
Ref: https://snyk.io/test/npm/gif-frames/1.0.1

This can be fixed by just upgrading the versions of get-pixels and save-pixels to their latest versions.
This PR updates these libraries.

[benwiley4000]

Hey, so we're those changes I had made in those libraries merged upstream to get pixels and save pixels? Sorry, it's been awhile since I looked at this.