Use .sortedKeys for JSONEncoder, so output is stable

[m4p]

When using swift-package-list as part of our toolchain, JSON output often changes despite the licenses not changing.

It seems .prettyPrint keys aren't sorted, and so the order of the JSON keys can fluctuate. I'd propose using .sortedKeys instead, so we can store the json in our git without generating superfluous changes.

[m4p]

(Happy to fix the failing test, if you agree with this change)

[FelixHerrmann]

Hi, thanks for your contribution! That's def. a reasonable thing to add, interestingly it was never a problem in the project where I use this tool (had id configured as Run Script + file in source control before switching to SPM plugin). I don't want to get rid of the .prettyPrinted option tho because it really helps readability (especially in commits). Please adjust this and then we can get this change in; tests should also not fail after that change!

[m4p]

Sure thing! Did just push the change.

[FelixHerrmann]

Looking good now, thanks for the adjustments. Will release that shortly!