Add missing apt update to nginx docker build.

docker/nginx/Dockerfile

@@ -3,6 +3,7 @@ FROM nginx
 RUN rm /etc/nginx/conf.d/default.conf
 COPY nginx.conf /etc/nginx/conf.d
 
+RUN apt update
 RUN apt install -y libjs-bootstrap4 fonts-font-awesome libjs-jquery libjs-popper.js libjs-jquery-datatables
 
 RUN mkdir /srv/media