title: Loopback model definition is not adding foreign key relation in database table
body: <p>I am using loopback for API design and data modeling. I am using MySQL as my database. Although my API rest URL successfully returns results e.g. <code>/states/{id}/cities</code>. I have following model but it seems no foreign key relation is added. Following are my model definition.</p>
  
  <pre><code>"state": {
    "options": {
      "relations": {
        "cities": {
          "type": "hasMany",
          "model": "city",
          "foreignKey": "stateId"
        }
      }
    },
    "properties": {
      "name": {
        "type": "string"
      }
    },
    "public": true,
    "dataSource": "db",
    "plural": "states"
  },
  "city": {
    "options": {
      "relations": {
        "state": {
          "type": "belongsTo",
          "model": "state",
          "foreignKey": "stateId"
        }
      }
    },
    "properties": {
      "name": {
        "type": "string"
      }
    },
    "public": true,
    "dataSource": "db",
    "plural": "cities"
  }
  </code></pre>
  
  <p>and below is screenshot of city table. 
  <img src="https://i.stack.imgur.com/yGqOF.png" alt="enter image description here"></p>
  
  <p>And following is State table screenshot.
  <img src="https://i.stack.imgur.com/OH1na.png" alt="enter image description here"></p>
  
  <p>I may be doing it wrong here. Looking forward for any pointers.</p>