fix: add missing App export (#640)

Author: kiroushi

src/apis/index.ts

@@ -29,7 +29,7 @@ export * from './watch'
 export * from './computed'
 export * from './inject'
 export { useCssModule, useCSSModule } from './useCssModule'
-export { createApp } from './createApp'
+export { App, createApp } from './createApp'
 export { nextTick } from './nextTick'
 export { createElement as h } from './createElement'
 export { warn } from './warn'