Amp-selector script attributes error

Problem/Motivation

When adding the amp/amp-selector library to the page and checking for amp errors, it can be identified that AMP does not recognize the amp-selector script defined in amp.libraries.yml.
Visible errors:

• You cannot include custom JavaScript.
• You must include the JavaScript extension 'amp-selector' for the 'amp-selector' tag.

Proposed resolution

Change the custom-template attribute defined in amp.libraries.yml for the amp-selector library to the custom-element attribute.
So the correctly loaded script would be:

<script async custom-element="amp-selector" src="https://cdn.ampproject.org/v0/amp-selector-0.1.js"></script>

and not like this:

<script async custom-template="amp-selector" src="https://cdn.ampproject.org/v0/amp-selector-0.1.js"></script>

See AMP documentation: https://amp.dev/documentation/components/amp-selector/