add staticClass and style to migration guide

vuejs/docs@6cc3c7a#diff-aa744c862c8dae7617ad8685224b3f8e80bed656707d8716b00b9e9069789a51

Author: naokie

src/guide/migration/render-function-api.md

@@ -103,8 +103,10 @@ export default {
 ```js
 // 2.x
 {
-  class: ['button', 'is-outlined'],
-  style: { color: '#34495E' },
+  staticClass: 'button',
+  class: {'is-outlined': isOutlined },
+  staticStyle: { color: '#34495E' },
+  style: { backgroundColor: buttonColor },
   attrs: { id: 'submit' },
   domProps: { innerHTML: '' },
   on: { click: submitForm },
@@ -119,8 +121,8 @@ export default {
 ```js
 // 3.x での構文
 {
-  class: ['button', 'is-outlined'],
-  style: { color: '#34495E' },
+  class: ['button', { 'is-outlined': isOutlined }],
+  style: [{ color: '#34495E' }, { backgroundColor: buttonColor }],
   id: 'submit',
   innerHTML: '',
   onClick: submitForm,