feat(elevator): add change event(#1826)

src/packages/__VUE/elevator/doc.en-US.md

@@ -481,7 +481,7 @@ app.use(Elevator);
 |-------|----------|-------------|
 | click-item | Click content | key: string, item: { id: 0, name: '' } |
 | click-index | Click index | key: string |
-| change | Change index | index: number |
+| change | Change index | index: number |   
 
 ### API