fix(config): only take default export

Author: pi0

src/build.ts

@@ -30,8 +30,9 @@ export async function build(
   // Create jiti instance for loading initial config
   const jiti = createJiti(rootDir, { interopDefault: true });
 
-  const _buildConfig: BuildConfig | BuildConfig[] =
+  let _buildConfig: BuildConfig | BuildConfig[] =
     (await jiti.import("./build.config", { try: true })) || {};
+  _buildConfig = (_buildConfig as any).default || _buildConfig;
   const buildConfigs = (
     Array.isArray(_buildConfig) ? _buildConfig : [_buildConfig]
   ).filter(Boolean);