fixes the updating process bug related with #91

[ttuygun]

Fixes https://github.com/objective-see/LuLu/issues/91

The default updating URL depends on https://objective-see.com/products.json but it's no longer up-to-date in contrast with github. For this reason, I changed the updating url as github using github's public API. I also changed objectForKey methods according to new URL.

Here's the working example. In this example, I'm on 1.1.0 and program says 1.1.1 is available.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Tarık Taha Uygun seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[jonathancross]

@ttuygun you need to sign the CLA and rebase, otherwise this can't be merged. (I don't know if it will be merged though)

[jamesalfei]

Is there any way we can get this PR progressed at all? Even if it means closing this PR and getting another contributor (like myself) to raise the changes? It seems the author is not active on this project at all.