Fix rounding issue with humane.js (i.e. 60 minutes)

Linked Meta topic: [“24 hours” Timestamp Should Probably Be “1 day”](http://meta.discourse.org/t/24-hours-timestamp-should-probably-be-1-day/4643)

Simple rounding issue. I've just patched it in Discourse, but I'll make a note to submit a PR to the source project as well.