please upgrade dependency on tantivy

[jonassmedegaard]

Hi,

Tantivy has seen some recent upgrades, helping to generally modernize dependency crates (which simplifies getting this project included with Debian).

Please consider upgrading to tantivy v0.21.1

[jonassmedegaard]

...and while at it, upgrade base64 as well.

[joepio]

will do

[joepio]

Done!