fix typed.js URL

[thesosa]

Fix

Replaces the link to the typed.js script with a new one because the current one is broken and so the typing animation in the landing page does not start.

Fixes #1969

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.

[wren]

Good catch. Thank you!

[wren]

Note: The failing CI in this depends on #1971 to fix.

[wren]

@thesosa Thanks for your patience!