The exit status code '1' says something went wrong:
stderr: "xvfb-run: error: Xvfb failed to start
"
stdout: ""
command: xvfb-run -- /usr/bin/wkhtmltopdf --lowquality --margin-bottom '10mm' --margin-top '10mm' --orientation 'portrait' --page-size 'a4' '/tmp/knp_snappy6811cbf4738ac3.97320030.html' '/tmp/knp_snappy6811cbf473c588.47680326.pdf'.
