'x' in modal close renders as strange capital A and hyphen

[phil-dileo]

replace x with × here https://github.com/cgross/angular-prompt/blob/6de8bdfdaa8862488f6deb53c5e5233ac6e77129/dist/angular-prompt.js#L109

Note: this is what bootstrap does http://getbootstrap.com/javascript/#static-example

I can submit a pull request for the small change.

[cgross]

A PR would be great. Thanks.