Do not crash GHA when Vercel domain aliasing fails

[Vadorequest]

Currently, if the Vercel aliasing fails during Github Action, the whole build is aborted.

It's not how it should work, aliasing my fail for various reasons and that shouldn't stop a team from working properly. It'd be fine not to have the alias but still continue the build, and run E2E/LH tests.

Also, it makes believe the deployment has failed, but it's not true. When aliasing fails, only the alias fails, Vercel did deploy correctly, though.

npx now alias $ZEIT_DEPLOYMENT_URL $ZEIT_DEPLOYMENT_ALIAS --token $ZEIT_TOKEN

Therefore, there is nothing stopping us from considering the aliasing part as optional, and take mesure from stopping the whole build when it fails.

[Vadorequest]

Builds will no longer crash when Vercel aliasing fails. See #180

Next step is to change the github comment when the aliasing fails, I tried a few things but wasn't able to do it. (not familiar enough with bash)

@Demmonius FYI