chore: remove beta reference in readme

Author: yyx990803

README.md

@@ -36,7 +36,7 @@ In addition, Vite is highly extensible via its [Plugin API](https://vitejs.dev/g
 
 ## Migrating from 1.x
 
-Vite is now in 2.0 beta. Check out the [Migration Guide](https://vitejs.dev/guide/migration.html) if you are upgrading from 1.x.
+Check out the [Migration Guide](https://vitejs.dev/guide/migration.html) if you are upgrading from 1.x.
 
 ## Packages