Custom post registration causing errors

There are many small problems with this code (see my comments below):

function gt_custom_post_type() {
  register_post_type('project',
    array(
      'rewrite' => array('slug' => 'projects'),
      'labels' => array(
        'name' => 'Projects', // <- missing comma
        'singular_name' => 'Project', 
        'add_new_item' => 'Add New Project',
        'edit_item' => 'Edit Project'
      ),
      'menu-icon' => 'dashicons-media-document',
      'public' => true,
      'has_archive' => true,
      'supports' => array(
        'title', 'thumbnail', 'editor', 'excerpt', 'comments' // <- thumbnail not thumnail
      )
    )
  );
}
add_action('init', 'gt_custom_post_type');

Also you’re lacking any internationalization in there…