Updating dockerfile for release v1.2.0

docker/1.2/Dockerfile

@@ -34,7 +34,7 @@ VOLUME /var/lib/mysql
 WORKDIR /mattermost
 
 # Copy over files
-ADD https://github.com/mattermost/platform/releases/download/v1.2.0-rc2/mattermost.tar.gz /
+ADD https://github.com/mattermost/platform/releases/download/v1.2.0/mattermost.tar.gz /
 RUN tar -zxvf /mattermost.tar.gz --strip-components=1 && rm /mattermost.tar.gz
 ADD config_docker.json /
 ADD docker-entry.sh /