fix(regexp): make it work with json strings that include quotes

Hi, I'm using this module as a method to get JSON.stringify with single quotes. It works great, but there is one problem with stuff like this:` {"a": "<a href=\"addr\">"}` because of the escaped double quotes inside the string. It seems you intended to handle this by unescaping double-quotes, but there was a problem with the top regexp that extracts string expression. What do you think? Does this make sense?