oEmbed short URL https issue

[nicolaasmatthijs]

When using oEmbed with a short URL (e.g. http://youtu.be/JrtWhFtjXTA) on an HTTPS page, the following error will be shown in most browsers:

[blocked] The page at 'https://cam.oae.com/content/cam/ZyxdB0wkZ' was loaded over HTTPS, but ran insecure content from 'http://api.longurl.org/v2/expand?callback=jQuery2000707950760377571_1406681916540&url=http%3A%2F%2Fyoutu.be%2FJrtWhFtjXTA&format=json': this content should also be loaded over HTTPS.

The attached pull request just ensures that the onError callback is called when the request to api.longurl.org fails, making sure that the client can appropriately react to the failure.

Unfortunately, there is no https version of api.longurl.org, so it's not possible to use that instead. An ideal solution would put something in place that allows this to work over https as well. However, this PR would still be useful to have in place regardless in case api.longurl.org were to go down temporarily.

[LGCambra]

The NFL would like to continue support for this plugin. Please re-submit your pull request with https://github.com/nfl/jquery-oembed-all. Thank you.