Numerical pages should be sorted as numerics not strings

[camfindlay]

Reported by Luke Percy over in the docs.silverstripe.org repo.

"The versioning order on http://doc.silverstripe.org/en/changelogs/ doesn't look right.
3.1.12 is the latest to my understanding (then RC,Alpha,Beta etc.), but the ordering on that list puts it below 3.1.9 this can be confusing to clients when reading what version is the latest."