vue-types: shape.loose does not work

Hi again, I noticed that shape({}).loose does not work. I did some digging and noticed that the unit test is actually incorrect.

I adapted the test to be breaking:

   it('should validate an object with keys NOT present in the shape on `loose` mode', () => {

      const customType = VueTypes.shape(shape).loose
      expect(customType.validator({
        id: 10,
        name: 'John',
        newProperty: true
      })).toBe(true)
    })

Test result:

WARN: '[VueTypes warn]: object is missing "newProperty" property'
[...]
SUMMARY:
✔ 76 tests completed
✖ 1 test failed

FAILED TESTS:
  VuePropTypes
    `.shape`
      ✖ should validate an object with keys NOT present in the shape on `loose` mode
        PhantomJS 2.1.1 (Mac OS X 0.0.0)
      Expected false to be true
      assert@test/index.spec.js:734:27
      toBe@test/index.spec.js:2615:28
      test/index.spec.js:5672:15

The problem is that you use objectAssign({ isLoose: true }, this) (see here). You create a new object, instead of appending data to this, you create a new object. This object is however not the one which is bound to the .shape() function. If loose would set this.isLoose=true, it is fixed, but I think the new object is actually intended behavior (that’s why this is not a PR).

Actually the fix from https://github.com/dwightjack/vue-types/issues/5 is the problem, because this binds the context of the validator function.