Hotfix for icons not showing

Hotfix for a known issue in the plugin. Solution taken from [here](umdevelopera#13 (comment))

includes/admin/class-admin.php

@@ -275,7 +275,7 @@ public function save_metaboxes_data( $post_id, $post, $update ) {
 			$color = isset( $input['_color'] ) ? sanitize_hex_color( $input['_color'] ) : '';
 			update_post_meta( $post_id, '_color', $color );
 
-			$icon = isset( $input['_icon'] ) ? sanitize_key( $input['_icon'] ) : '';
+			$icon = isset( $input['_icon'] ) ? wp_strip_all_tags( $input['_icon'] ) : '';
 			update_post_meta( $post_id, '_icon', $icon );
 
 			$position = isset( $input['_position'] ) ? absint( $input['_position'] ) : '';