List of "potentially open issues" should be based on last modification time, not creation

[jdm]

Issues like servo/servo#6888 appear there even thought there's been activity quite recently.

[edunham]

According to https://developer.github.com/v3/issues/ , this will probably be a matter of changing the created parameter to updated in the getPotentiallyOpenIssues and getOoenIssues functions in site.js

[mfeckie]

@jdm Can this issue be closed now?

[jdm]

Yes!