avoid problems with caching of apt-get operations

services/filestore/Dockerfile

@@ -1,5 +1,4 @@
 FROM node:6.9.5
 
-RUN apt-get update
 # we also need imagemagick but it is already in the node docker image
-RUN apt-get install -y --no-install-recommends ghostscript optipng
+RUN apt-get update && apt-get install -y --no-install-recommends ghostscript optipng