title: Cannot find name "MAT_DATE_LOCALE" with Material.angular Datepicker
body: <p>According to the documentation <a href="https://material.angular.io/components/datepicker/overview" rel="noreferrer">https://material.angular.io/components/datepicker/overview</a> here to set the locale code to one you want you provide it by putting </p>
  
  <pre><code>providers: [
      {provide: MAT_DATE_LOCALE, useValue: 'en-GB'},
  ]
  </code></pre>
  
  <p>But then my app won't compile as it tells me it cannot find the name MAT_DATE_LOCALE. Am I missing something here as in I have to define it myself? Though, I can't think of where to put it as it's all in the module class. </p>