README: use badges from Gitlab instead of Travis/Coveralls

11 jobs for travis_fixes in 6 minutes and 13 seconds (queued for 9 seconds)
Status Job ID Name Coverage
  Build
passed #94778
docker linux amd64
build:linux:amd64

00:00:26

 
  Test
passed #94782
docker linux amd64
deckard:linux:amd64

00:05:28

passed #94781
docker linux amd64
installcheck:linux:amd64

00:00:29

passed #94783
docker linux amd64
installcheck:valgrind:linux:amd64

00:00:52

passed #94779
docker
lint:lua

00:00:24

passed #94786
docker linux amd64
respdiff:iter:tcp:linux:amd64

00:01:54

passed #94787
docker linux amd64
respdiff:iter:tls:linux:amd64

00:02:03

passed #94785
docker linux amd64
respdiff:iter:udp:linux:amd64

00:02:06

passed #94780
docker linux amd64
test:linux:amd64

00:00:36

passed #94784
docker linux amd64
test:linux:amd64:valgrind

00:00:26

 
  Coverage
passed #94788
docker linux amd64
coverage

00:00:17

68.7%