Convert double quotes to single quotes in moment.js

Convert double quotes to single quotes for consistency throughout moment.js file.

All tests completed without any errors.

![screen shot 2014-07-06 at 10 22 19 am](https://cloud.githubusercontent.com/assets/3654181/3489502/26ba91de-0532-11e4-83c9-56d6a68f4187.png)

![screen shot 2014-07-06 at 10 22 50 am](https://cloud.githubusercontent.com/assets/3654181/3489504/2e2c79c8-0532-11e4-8323-9bf10f17326d.png)