Use official aptly repository

Dockerfile

@@ -1,7 +1,10 @@
 FROM debian:stretch
 MAINTAINER Benjamin Bohard
 
-RUN apt update && apt install -y ca-certificates gnupg aptly aptly-publisher && apt clean
+RUN apt update && apt install -y ca-certificates gnupg && apt clean
+COPY aptly.sources.list /etc/apt/sources.list.d/aptly.list
+RUN apt-key adv --keyserver pool.sks-keyservers.net --recv-keys ED75B5A4483DA07C
+RUN apt update && apt install -y aptly && apt clean
 
 VOLUME ["/signing-key", "/packages"]
 EXPOSE 8080

aptly.sources.list

@@ -0,0 +1 @@
+deb http://repo.aptly.info/ squeeze main