Make Buffer button appear sooner

Trello task: https://trello.com/c/VMJilPXE

To test, go to joel.is and click the Tweet button - note that the Buffer button takes around 5 secs to appear.

Then, copy the updated embeds/buffer-twitter.js to the appropriate place in your installed extension (~/Library/Application Support/Google/Chrome/Default/Extensions/noo[...]bhh/2.3.10_0/data/shared/embeds/buffer-twitter.js for me!) then disable and re-enable the extension.

Now, visiting joel.is, and clicking the Tweet button should give a much more snappy Buffer button.

The diff looks worse than it really is. I basically played with the timeouts at the bottom a little and rearranged the order the buttons are attempted to be inserted.