title: How to format the ruby model level errors
body: <p>I am using mongodb. I implemented some model level validations, and the error message comes in an array format like:</p>
  
  <pre><code>{
    "first_name": [
      "is invalid"
    ],
    "last_name": [
      "is invalid"
    ]
  }
  </code></pre>
  
  <p>I want to change this to string format like this:</p>
  
  <pre><code>{
    "first_name": "is invalid",
    "last_name": "is invalid"
  }
  </code></pre>
  
  <p>What do I do?</p>