Switch to Citus-owned package repo

Rebuilding older tags is impossible if we use PGDG, which doesn't (yet)
retain previous package versions. By using our packagecloud.io repo, we
can ensure tags remain buildable as long as we keep the packages.

Dockerfile

@@ -1,11 +1,16 @@
 FROM postgres:9.5.3
 MAINTAINER Citus Data https://citusdata.com
 
-ENV CITUS_VERSION 5.1.0-1.pgdg80+1
+ENV CITUS_VERSION 5.1.0-1
 
 # install Citus
 RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+       ca-certificates \
+       curl \
+    && curl -s https://install.citusdata.com/community/deb.sh | bash \
     && apt-get install -y postgresql-$PG_MAJOR-citus=$CITUS_VERSION \
+    && apt-get purge -y --auto-remove ca-certificates curl \
     && rm -rf /var/lib/apt/lists/*
 
 # add citus to default PostgreSQL config

nightly/Dockerfile

@@ -1,14 +1,12 @@
 FROM citusdata/citus:latest
 MAINTAINER Citus Data https://citusdata.com
 
-# install citus nightly from packagecloud
+# switch to Citus nightly
 RUN apt-get update \
-    && apt-get install -y --no-install-recommends ca-certificates curl \
-    && curl -s -O \
-       https://packagecloud.io/install/repositories/citusdata/community-nightlies/script.deb.sh \
-    && chmod +x script.deb.sh \
-    && ./script.deb.sh \
-    && rm -f script.deb.sh \
-    && apt-get install -y postgresql-9.5-citus \
+    && apt-get install -y --no-install-recommends \
+       ca-certificates \
+       curl \
+    && curl -s https://install.citusdata.com/community-nightlies/deb.sh | bash \
+    && apt-get install --only-upgrade -y postgresql-$PG_MAJOR-citus \
     && apt-get purge -y --auto-remove ca-certificates curl \
     && rm -rf /var/lib/apt/lists/*