Skip Forward/Backward 20s buttons are missing labels(AV)

[LanieOkorodudu]

UV version:
v4.2.1

I'm submitting a:

• bug report => please fork one of these codesandbox examples with a repro of your issue and include a link to it below
• feature request => please use the user stories repo
• support request => Please do not submit support requests here, use stackoverflow

Current behavior:
The video player’s skip forward and skip backward (20 seconds) buttons are currently not labelled.

Expected behavior:
The video player’s skip forward and skip backward (20 seconds) controls are currently not labeled.

Steps to reproduce:

1. Play this AV manifest: https://iiif.io/api/cookbook/recipe/0064-opera-one-canvas/manifest.json
2. Move your cursor over the player controls.
3. Check the skip forward and skip backward buttons.

[demiankatz]

It may be worthwhile to double check whether upgrading MediaElement in #1298 makes a difference to this issue.