Change center crop to be only 88 percent of available width/height

[jtklein]

The center crop yields better vision scores if the overall size of the center square is reduced to be that of 88% of the original frame of an uncropped range. So, if the original frame is 1000x2000 pixel the center square should be the center 880x880 pixel.

[jtklein]

This #22 introduces a param to set the crop ratio as an option. Works on Android only though at the moment.

[jtklein]

On iOS the best way forward is probably to use https://github.com/mrousavy/vision-camera-resize-plugin in vision-camera v3.