`isBrowser` should (probably) be `isBrowser()` in hi-res-timestamp.ts

[jeffpeck10x]

See here:
https://github.com/uber-web/probe.gl/blob/master/modules/log/src/utils/hi-res-timestamp.ts#L8

The imported isBrowser is a function that returns a boolean. It looks like that should be called isBrowser()

[ibgreen]

I think it is actually exported as a constant: https://github.com/uber-web/probe.gl/blob/master/modules/env/src/utils/globals.ts#L9

I agree this can be confusing. We do export a similar constant from most of the vis.gl frameworks and I think it may indeed a function in one of them, which only adds to the confusion.