[html-tests] Add some tolerance to lastModified test (#1236)

Both [Servo](https://github.com/servo/servo/issues/3228) and [Gecko](https://bugzilla.mozilla.org/show_bug.cgi?id=1064625) are getting errors where the test seems to be off by a second.

It seems like a bug in the implementation, but it might also be an issue with the test. This allows for some leeway when it comes to comparing the times.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/1236

Received on Tuesday, 9 September 2014 09:16:45 UTC