Currently, to align images only Right & Left options are available as shown in below image:
How to Enable full-width images similar to the link which is displaying images: https://medium.com/perspectives-from-the-economist-intelligence-unit/lake-chads-twofold-crisis-27545789e9d7
With CK Editor Module. Install CK EDITOR Image module, which enables the third alignment option to center the image also.
Here is the link to download the Module. https://www.drupal.org/project/ckeditor_image
Note: CK EditorImage only supports for Drupal 7 and its previous versions.
