allow node process to start on low port 80

Fixes #503

Dockerfile

@@ -33,6 +33,7 @@ RUN export DEBIAN_FRONTEND=noninteractive \
       libegl1 \
       xvfb \
       xauth \
+      libcap2-bin \
   && apt-get -y --purge autoremove \
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/*
@@ -46,6 +47,9 @@ ENV CHOKIDAR_INTERVAL=500
 VOLUME /data
 WORKDIR /data
 
+# allow node to listen on low ports
+RUN setcap 'cap_net_bind_service=+ep' /usr/local/bin/node
+
 EXPOSE 80
 
 USER node:node