Fix object prop default error

[zwubs]

Problem

When using the module through npm an error occurs stating:

[Vue warn]: Invalid default value for prop "option": Props with type Object/Array must use a factory function to return the default value.

Solution

Within 'waterfall.vue' changing the 'option' prop to state this:
default: () => {}
rather than this: default: {}

Files Changed

• waterfall.vue: Updated line 15 to previously mentioned code.
• vue2-waterfall.js: Rebuilt file to incorporate aforementioned changes.