workaround docker image issue

npm/cli#5900

Dockerfile

@@ -2,7 +2,8 @@ FROM node:alpine
 RUN apk add --no-cache ffmpeg
 WORKDIR /app
 COPY package.json .
-RUN npm install --omit=dev
+RUN npm install --omit=dev \
+ && chown -R $(id -u):$(id -g) node_modules # workaround for https://github.com/npm/cli/issues/5900
 COPY lib lib
 WORKDIR /data
 CMD ["node", "/app"]