Use simplified entrypoint script

docker-entrypoint.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+set -e
+
+if ! which -- "${1}"; then
+  # first arg is not an executable
+  xvfb-run --server-args="-screen 0 1024x768x24" -- node /app/ "$@"
+  exit $?
+fi
+
+exec "$@"