Run Docker containes as non-root user

docker/Dockerfile

@@ -32,6 +32,9 @@ ENV VIPS_WARNING=0
 ENV MALLOC_ARENA_MAX=2
 ENV LD_LIBRARY_PATH /usr/local/lib
 
+RUN groupadd -r imgproxy && useradd -r -g imgproxy imgproxy
+USER imgproxy
+
 CMD ["imgproxy"]
 
 EXPOSE 8080