Invalid CDN link to plugins produced in samples listings

[mlewand]

Provide detailed reproduction steps (if any)

1. Open Abbreviation Plugin sample.
2. Scroll down to "Get Sample Source Code" section.
3. Click it.
4. Inspect the URL of abbr plugin.

Expected result

CKEDITOR.plugins.addExternal( 'abbr', 'https://sdk.ckeditor.com/samples/assets/plugins/abbr/', 'plugin.js' );

Actual result

CKEDITOR.plugins.addExternal( 'abbr', 'https://sdk.ckeditor.com/https://sdk.ckeditor.com/samples/assets/plugins/abbr/', 'plugin.js' );