using sharp instead of gm as image processor

[ekoeryanto]

Found my self struggling with Error: Stream yields empty buffer on windows 10.
I think it's better to use the more cross-platform image processor

Thanks.

[KaelWD]

Sharp doesn't support GIF output, so we'd have to use PNG or JPEG instead. I can certainly add an option to use a different processor, but the results will not be nearly as good.
The error may be related to aheckmann/gm#559, I haven't actually tried gm on windows yet.

[ekoeryanto]

thinking about multi image processor support, maybe vuetify-loader/sharp-loader.js

I think aheckmann/gm#559 should be on the README.
installed with scoop that already appended all the binary of imagemagick to the PATH does not work, but installed manually with the install legacy utilities ticked works.