refactor: improve consistency

Author: sxzz

src/fake-js.ts

@@ -297,7 +297,7 @@ export function createFakeJsPlugin({
 
       const str = s.toString()
       if (str.trim().length === 0) {
-        return 'export {}'
+        return 'export { };'
       }
 
       return str

tests/rollup-plugin-dts/export-empty-object/known-diff.patch

@@ -1,2 +1,2 @@
 // index.d.ts
-export {}
+export { };