gomod: update zoekt to include graceful shutdown

Created by: keegancsmith

zoekt-webserver now handles SIGINT and SIGTERM to gracefully shutdown. This is an attempt to remove the "Readiness probe failed" events on Sourcegraph.com when rolling out a new version of Zoekt.

Zoekt commits:

• https://github.com/sourcegraph/zoekt/commit/58ac958 zoekt-webserver: graceful shutdown on SIGINT and SIGTERM
• https://github.com/sourcegraph/zoekt/commit/180b044 indexserver: set repoid via BuildOptions.RawConfig
• https://github.com/sourcegraph/zoekt/commit/2ff16f3 indexserver: Add an endpoint to enqueue a repo index