Amend `Flamsteed#_addMetaData` `t` assignment
* Use `Date.now()` instead of `window.performance.now()` due to `window.performance.now()` returns seconds from `navigationStart`
Syntax amend for attribute presence check
Merge pull request #12 from marckysharky/master

Amend `Flamsteed#_addMetaData` `t` assignment