Switch Twitter oEmbed to SSL due to a Twitter API change that broke embedding across all WordPress sites.

Merges [26967] to the 3.8 branch.

props yurivictor, cojennin.
fixes #26844.


git-svn-id: https://develop.svn.wordpress.org/branches/3.8@26969 602fd350-edb4-49c9-b593-d223f7449a82