configure.ac: Bump version to 1.20

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
2 jobs for master in 40 seconds (queued for 1 second)
Status Job ID Name Coverage
  Containers Build
passed #1779794
container_build

00:00:19

 
  Test
passed #1779795
test

00:00:21