fix: missing slash in copy as curl

[markphelps]

Fixes copy as curl URL:

curl -X POST -H "Content-Type: application/json" -H "Accept: application/json" -H "Cache-Control: no-store" -H "Authorization: Bearer <api-token>" -d '{"flagKey":"asdfasdf","entityId":"d0b0a86d-d63c-403a-a5cd-35517283992d","context":{},"namespaceKey":"default"}' https://try.flipt.ioevaluate/v1/variant

Note https://try.flipt.ioevaluate/v1/variant should be https://try.flipt.io/evaluate/v1/variant

[erka]

It looks great.

This bug I introduced in #2723 just for the record.