Update tweetable-text.php

In some browsers (depending on JS interpreter in it) the other jQuery apps (if present) don't work anymore and this error appears:  "Uncaught TypeError: Property '$' of object [object Object] is not a function"
The "$" inside ready(function()) set the alias for jQuery as you can read at the middle of the page of this article: http://codex.wordpress.org/Function_Reference/wp_enqueue_script