chore(registry): bump version

In preparation for making an upstream PR, I rebased it against
upstream's master.

Author: Matthew Fisher

registry/Dockerfile

@@ -15,7 +15,7 @@ RUN useradd -s /bin/bash registry
 # add the docker registry source from github
 RUN git clone https://github.com/deis/docker-registry /docker-registry && \
     cd /docker-registry && \
-    git checkout 190e03f && \
+    git checkout 3a192af && \
     chown -R registry:registry /docker-registry
 
 # install boto configuration