Redirect /docs/ to /docs/current/

**Describe the bug**

Expectation:
* Going to https://fishshell.com/docs/ and seeing fish documentation

Actually happening:
* https://fishshell.com/docs/ gives a 404

Proposed solution:
* Have https://fishshell.com/docs/ redirect to https://fishshell.com/docs/current/

Start by locating the fish-site routing or hosting configuration responsible for serving /docs/. Verify that requests to https://fishshell.com/docs/ redirect to https://fishshell.com/docs/current/ and confirm the redirect resolves without a 404.

Written by the indexing model from the issue text.