Fixes JS type error on one of the examples and changes all quotation marks to double for consistency

For more details, check line 197: https://github.com/viljamis/enquire.js/pull/new/WickyNilliams:gh-pages...viljamis:gh-pages#L0L197

The example on the site gave me some headache as it had typo on it and I couldn't instantly spot what's wrong. I also changed all of the quotation marks to double ones for consistency, as most of the code examples were already using double and not single ones.