Use 'master' for 'stable' docker build tag

Author: lloydwatkin

Dockerfile

@@ -14,7 +14,7 @@ RUN apt-get upgrade -y
 RUN apt-get install -y --no-install-recommends git git-core libicu-dev libexpat-dev build-essential libssl-dev build-essential g++
 
 RUN git clone https://github.com/buddycloud/buddycloud-http-api.git api-server
-RUN cd api-server && git checkout develop
+RUN cd api-server && git checkout master
 RUN cd api-server && npm i . && cp contrib/docker/config.js .
 ADD contrib/docker/start.sh /data/