cannot set beautify to false.

[yezhongqiang]

beautify option in bootstrap token is true by default, if users want to set it to false, it doesn't work because this code:
/*
Appends only truthy values that are not promises.
*/
_appendOption: function(options, attributeName) {
let attrValue = this.get(attributeName);
if (attrValue && typeof attrValue.then !== 'function') {
options[attributeName] = attrValue;
}
return options;
},

attrValue will be false when set beautify to be false, then the if check will by pass the assignment, which causes unable to set beautify option.