Adding in ability to switch release channel without restarting Hyper

[KevinRizzoTO]

This is to address #2351

This code seems to run properly. However, it is difficult to fully test without a Mac Developer ID. I didn't realize that these licenses require a yearly subscription ☹️. So far if I try to build this as a package and change the autoUpdater channel I receive errors that the app is not code-signed. If someone with one of these licenses could give this a quick test that would be great!

[qkdreyer]

I've successfully managed to build your fork using yarn run dist, and here is the output from running the freshly compiled Hyper.app :

TRIOMBP:hyper qkdreyer$ ./dist/mac/Hyper.app/Contents/MacOS/Hyper 
Plugin hyper-transparent (1.1.3) loaded.
Plugin hyper-startup (0.2.0) loaded.
Plugin hypercwd (1.1.1) loaded.
running in prod mode
electron will open file:///Users/qkdreyer/Projects/hyper/dist/mac/Hyper.app/Contents/Resources/app.asar/index.html
2017-11-08 10:21:52.757 Hyper[13220:2818107] *** WARNING: Textured window <AtomNSWindow: 0x7ff42cef3d20> is getting an implicitly transparent titlebar. This will break when linking against newer SDKs. Use NSWindow's -titlebarAppearsTransparent=YES instead.
Checking for notification messages
No matching notification messages
2017-11-08 10:22:11.480 Hyper[13220:2818113] Download completed to: file:///Users/qkdreyer/Library/Caches/co.zeit.hyper.ShipIt/update.07cYpjp/hyper-2.1.1-mac.zip
Error fetching updates Code signature at URL file:///Users/qkdreyer/Library/Caches/co.zeit.hyper.ShipIt/update.07cYpjp/Hyper.app/ did not pass validation: le code n’est pas conforme aux exigences de code spécifiées (Error: Code signature at URL file:///Users/qkdreyer/Library/Caches/co.zeit.hyper.ShipIt/update.07cYpjp/Hyper.app/ did not pass validation: le code n’est pas conforme aux exigences de code spécifiées)

[chabou]

@KevinRLeC Thank you so much for this PR 🙏

Indeed this is really hard to test this type of feature. Mac Developer ID is not enough. Only Zeit certificate can sign this application. But I think that canary commit CI builds are signed.

Your code seems OK. What we can do is to merge your code into canary in order to have a signed version with your PR and test it: setting canaryChannel to 'stable' should directly check update and ask to install.

[chabou]

Tested with signed artefact generated by CircleCI.
I edited Hyper.app to fake its version number.
After editing config, it has directly downloaded canary release 😍

Really good job @KevinRLeC

[KevinRizzoTO]

Glad it worked @chabou keep up the great work with the product 😄