fix: [postgres] add required dependency of ``pgm``

``coreutils`` is required to install full ``sort`` implementation
with the ``-V`` option used by ``pgm``.

postgres/build/Dockerfile

@@ -30,7 +30,7 @@ RUN curl -L https://raw.githubusercontent.com/0k/pgm/0.0.6/bin/pgm > /bin/pgm &&
 
 FROM common
 
-RUN apk -U add pv python2 file sed
+RUN apk -U add pv python2 file sed coreutils
 
 COPY --from=builder /home/packager/packages/tmp/x86_64/*.apk /tmp/
 COPY --from=builder /bin/pgm /bin