title: Missing camera roll permission in expo
body: <p>I have "Change Image" button and I want to user camera roll to change the image.<br>
  But I get warning that I don't have permission to use camera roll.<br>
  How do I check if permission is granted or not? If it is not I want to ask for permission.  </p>
  
  <p>This is my code for now: </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>    _pickImage = async () =&gt; {
          let result = await ImagePicker.launchImageLibraryAsync({
            allowsEditing: true,
            aspect: [4, 3],
          });
      
          console.log(result);
      
          if (!result.cancelled) {
            this.setState({ image: result.uri });
          }
      };</code></pre>
  </div>
  </div>
  </p>
  
  <p>This may be very dumb question but I am bit confused here...</p>
  
  <p>If you need any more information please comment.</p>
  
  <p>Thanks! </p>