When concatenating multiple source map, each one need to have a specific source name,
otherwize it will the last source will erase the previous ones.
@param   {String} sourceFileName source file name original from options
@param   {String} code           code associated
@returns {String} a generated source file name unique form each codes
function(sourceFileName, code) {

    // If we're processing a block of code,
    // let's try to find a class name in the block to specify the sourceFileName

    var re = /class\s?([^\s]+)(\s?{|\s.*)|\s([^\s]+)\s?=\s?class/;
    var m = re.exec(code);

    return (sourceFileName || "") + (m && m[1] || nonce());
}