Fix test for timestamp precision in browser

[ewhauser]

#314 adds support for running browser tests under karma. There is an existing test in batch-record.test.js#should record duration in microseconds that has been disabled under this runner due to an error.

This error existing previously (we just didn't run it under CI), so it has been disabled for now. The error is likely due to the use of lolex or a math rounding issue that only presents itself in the browser.

[jcchavezs]

@ewhauser can you think on any actions to take from now?

[ewhauser]

I can try to debug this at some point in the near future. Likely some combination of browser precision, browserify, and/or lolex that cause that test not to function correctly. Given the fact that the rest of the coverage in that file works, I do not think this is a high priority issue as regressions would still continue to get caught on the NodeJS side.