deps: Move canvas to development dependencies

[kyranet]

More information about devDependencies here.

The reason for this change is that gifencoder does not seem to need the package canvas to work as shown in the addFrame lines, but rather checks for the existence of the method. However, I do not find any require('canvas') in the project (unless I'm missing something!) besides the example files and tests.

[relsqui]

I'd love it if this got merged, it's currently blocking me upgrading to 2.0.0 because I don't want to debug canvas's install failures in CI given that I don't actually need canvas. :)

[cenfun]

this is great, since "canvas" module was so big (65.74 MB) and it's not runtime dependency

[lostfictions]

would love for this to get merged!

[kyranet]

I really didn't want to come down to this, as I'm very against promoting my own code in similar packages, but since there's virtually no update in this repository, and this could help a lot of people, I have made a fork and is available at @skyra/gifenc.

I have rewritten the entire package to TypeScript (types are shipped in the package, no need for @types/), removed several global variables, improved performance across the board (2x speedup), all while keeping nearly 1:1 functionality and behaviour, it should be a drop-in replacement.