provision: Replace --production-travis with --build-release-tarball-only.

--production-travis was renamed to --build-release-tarball-only, both
  in master and in the 2.1.5 release.

Fixes #256.

Author: arpit551

Dockerfile

@@ -39,7 +39,7 @@ WORKDIR /home/zulip/zulip
 ARG CUSTOM_CA_CERTIFICATES
 
 # Finally, we provision the development environment and build a release tarball
-RUN ./tools/provision --production-travis
+RUN ./tools/provision --build-release-tarball-only
 RUN . /srv/zulip-py3-venv/bin/activate && \
     ./tools/build-release-tarball docker && \
     mv /tmp/tmp.*/zulip-server-docker.tar.gz /tmp/zulip-server-docker.tar.gz