screenshots.png: Compress the space to show off the colours more

[Jonta]

https://raw.githubusercontent.com/okraits/j4-make-config/master/screenshots.png

Is show in Readme

Vast amounts are uninformative blackness

(Also: Theme "google"'s bottom right terminal window is highlighted, which is inconsistent with the ones above)

One could probably make an Imagemagick-script to do this, but I think cropping in e.g. GIMP would be faster