types: add Popover typing

types/index.d.ts

@@ -65,6 +65,7 @@ export class Overlay extends VanComponent {}
 export class Pagination extends VanComponent {}
 export class Panel extends VanComponent {}
 export class PasswordInput extends VanComponent {}
+export class Popover extends VanComponent {}
 export class Popup extends VanComponent {}
 export class PullRefresh extends VanComponent {}
 export class Radio extends VanComponent {}