index.html: Update schedule due to COVID-19.
index.html: Update schedule due to COVID-19.

Due to COVID-19 TuxCon 2020 has to be postponed. Instead on 30-31
May we will live stream talks on open source topics.

Signed-off-by: Leon Anavi <be92910ae7bb6f58bb9b7c6f845bc30640119592@anavi.org>

TuxCon/tuxcon-website,TuxCon/tuxcon-website