Update Dockerfile

Dockerfile

@@ -56,7 +56,7 @@ RUN chmod a+x /usr/bin/xvfb-run
 USER root
 RUN export XVFBARGS="-screen 0 1280x1024x24" && \
     export DISPLAY=:99.0  && \
-    /usr/bin/xvfb-run && \
+    /etc/init.d/xvfb start && \
     sleep 3  && \
     curl -L https://download.qt.io/official_releases/qt/5.9/5.9.4/qt-opensource-linux-x64-5.9.4.run --output qt-opensource-linux-x64-5.9.4.run && \
     chmod +x qt-opensource-linux-x64-5.9.4.run && \