Validate json

[jimaek]

It would help a lot if the bot could validate update.json and comment any errors it finds.

[megawac]

jsdelivr/jsdelivr#1273

[megawac]

How comprehensive do you think this check should be @jimaek. If I spend time implementing this I'm probably going to make it report all the files that would be included from the last release (if the repo is a github one)

[jimaek]

The easiest check would be to simply check if the json is valid.
What other stuff did you want to include?

[megawac]

I'd probably do this one in conjunction with #26 and provide collabs with all the files that would be included if the next release contains the same files as the previous

[jimaek]

Currently my issue with update.json is the manual json verification that I need to do, If you can add this I will be a happy man :)
Except from that you can add anything else you want. This project is your baby :)