Add lxml to docker image for web previews
Add lxml to docker image for web previews

Signed-off-by: Paul Tötterman <7f588d170b73cf735638cbe158b4d6675233f7af@iki.fi>

matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse