use module.exports for mixins

package.json

@@ -1,6 +1,6 @@
 {
   "name": "vue-select",
-  "version": "1.1.3",
+  "version": "1.1.4",
   "description": "A Vue.js project",
   "author": "Jeff Sagal <sagalbot@gmail.com>",
   "private": false,

src/mixins/pointerScroll.js

@@ -1,4 +1,4 @@
-export default {
+module.exports = {
   methods: {
     /**
      * Adjust the scroll position of the dropdown list