docs: replace echo with return

Author: kenjis

user_guide_src/source/installation/upgrade_validations/002.php

@@ -13,11 +13,11 @@ public function index()
         if (! $this->validate([
             // Validation rules
         ])) {
-            echo view('myform', [
+            return view('myform', [
                 'validation' => $this->validator,
             ]);
-        } else {
-            echo view('formsuccess');
         }
+
+        return view('formsuccess');
     }
 }