title: Sails global doesn't work in helpers when using typescript
body: <p>I get <code>error TS2304: Cannot find name 'sails'.</code> when trying to use <code>sails</code> global inside a ts helper. The sails global is enabled in the configuration, and this works when I change it to js.
  This is my <code>api/helpers/is-admin-email.ts</code>. </p>
  
  <pre><code>module.exports = {
    friendlyName: 'Is admin email',
  
    description: 'Checks if the email is in admin email list',
  
    sync: true,
  
    inputs: {
      email: {
        type: 'string',
        example: 'example@email.com',
        description: 'the email to check with admin list',
        required: true,
      },
    },
  
    exits: {
      success: {
        description: 'Returns true if the email is in admin list',
      },
    },
  
    fn: function(inputs, exits) {
      const adminEmails: Array&lt;string&gt; = sails.config.custom.adminEmails;
      const isAdmin = adminEmails.includes(inputs.email);
      exits.success(isAdmin);
    },
  };
  </code></pre>
  
  <p>Note: the <code>sails</code> global works fine in ts controllers.</p>