fix: modified pattern for vimeo videos...

... so that relative URLs with "same protocol" also work.

Wordpress embeds vimeo videos like that:
```
<iframe src="//player.vimeo.com/video/14965306" width="640" height="360" frameborder="0" title="The Notwist - On Off The Record" webkitallowfullscreen mozallowfullscreen allowfullscreen>
```

With this modified pattern these embeds are also recognized by your great plugin.