Fix weirdness with arrays

list property will have Array type with an example like the following:

class Foo extends mixinObject() {
     static get props() {
          return {
             list: []
          };
     }
 }

var foo = new Foo();
foo.list = [ "one", "two" ]; 

TypeError: Right-hand side of 'instanceof' error will not be thrown.

#141