Use correct default for fetchData

`fetchData` was defaulting to a function that returns the `Promise.resolve` function, where it should be defaulting to a function that returns a resolved Promise (`Promise.resolve()`)

src/decorators/with-data.js

@@ -14,7 +14,7 @@ const DataMixin = require('../mixins/data-mixin');
  * for adding Aurora data fetching
  */
 module.exports = function({
-  fetchData = (() => Promise.resolve),
+  fetchData = (() => Promise.resolve()),
   dataProp = 'data',
   loadingProp = 'isLoading',
   disableServerLoading = false,