Stop ie8 from breaking with prism-core

[Pinpickle]

Can't say anything about plugins, but this stops IE8 from breaking (read some discussion at #9).
All I did was add a var statement to the declaration of self at the beginning of the file and IE stopped complaining. Nothing is broken, because that still makes it a global declaration.

Please ignore my typo about issue 8 in my commit message, git amend didn't work for some reason.

[Golmote]

Does it still work when used in a Worker?

[Pinpickle]

@Golmote I'm afraid I don't know and I'm not even sure how to test that. I'm fairly sure the new code means exactly the same thing, so this shouldn't change any functionality anywhere.

Happy to test with some instructions!

[Golmote]

You should be able to test it by adding the data-manual attribute on the script and then calling highlightAll(true) yourself. The async parameter should run Prism in a Worker.

[Pinpickle]

Tested it on Chrome, Firefox, Safari (Mac), and Chrome, IE11 (Windows). Everything looked to be working. An error was thrown about an undefined document (because workers don't have access to the DOM). I was getting these with or without the change in my tests so that's an issue for another day.

So yes, it works when used in a Worker.

[Joeynoh]

Came here to submit the same pull request. This issue keeps failing our IE tests on deploy, and now we cannot use a package manager to install Prism.