use object-assign ponyfill

src/shared/mergeComponentData.js

@@ -1,3 +1,5 @@
+import assign from 'object-assign'
+
 /**
  * Recursively shallow-merges component object with it's children component objects.
  * This function is responsible for obtaining the `this` context of metaInfo props when
@@ -9,7 +11,7 @@
 export default function mergeComponentData (component) {
   if (component.$children.length) {
     return component.$children.reduce((data, child) => {
-      return Object.assign({}, data, mergeComponentData(child))
+      return assign({}, data, mergeComponentData(child))
     }, component)
   }
   return component