Update document-register-element to 1.12.0
Before Mar 2019 (before Chrome 73), we should update document-register-element to 1.12.0 (or later) (currently using 1.3, released in Nov 2016 and introduced to GitLab in !9570 (merged)) to use window.customElements.define
instead of the deprecated document.registerElement
(see also https://www.chromestatus.com/features/4642138092470272).
Edited by Takuya Noguchi