README.md: JSON standard compliance in example

++ What: changing example JSON ```{hours12: false}``` to ```{"hours12": false}``` to comply with [The JSON Lexical Grammar](http://www.ecma-international.org/ecma-262/5.1/#sec-15.12.1.1)
++ Why: Copying the example without double quotes around the JSONString keyword (here: "hours12") to general JavaScript contexts will produce errors, see also [jQuery.parseJSON()](http://api.jquery.com/jquery.parsejson/)