trace throwing in production builds in MobX 6 is a breaking change

[quanganhtran]

In ea0b1d8, trace started throwing in production and this does not seem to be mentioned anywhere. Even if trace was never meant to be used in production, it ran just fine before so this should be marked as a breaking change.

This commit seemed to be a part of MobX 6 release. At least it did not throw in MobX 5.15.0

[quanganhtran]

Also I am not sure why it has to throw an error instead of being a noop

[kubk]

Thanks for the report. I've provided a fix. Let's wait until it is merged: #3709