It seems that there is a difference for the following object between v2.2.1 (it returns that it is the plain object) and v1.11.2 (it returns that it is not):

var parentObj = {foo: "bar"};
var childObj = Object.assign(Object.create(parentObj), {bar: "foo"});
jQuery.isPlainObject(childObj);

I think that 1.11.2 is correct.