Revert "custom mode result as string"

This reverts commit ec15d98.

Author: lgh06

packages/pptr/lib/customMode.mjs

@@ -24,7 +24,7 @@ async function customModeTask({ taskDetail, page }){
     // use vm to limit custom mode script's total time
     // vm is not safe
     let execResult = runFuncInVm({taskDetail, page, nodeFetch, fnString});
-    return String(execResult);
+    return execResult;
   } catch (error) {
     console.error(error);
     // TODO here is not so right