upgrade docker

Author: chrisgorgo

Dockerfile

@@ -1,4 +1,4 @@
-FROM docker:1.12
+FROM docker:1.13
 
 RUN apk add --update automake libtool m4 autoconf alpine-sdk linux-headers && \
     wget -qO- https://github.com/gmkurtzer/singularity/archive/2.1.2.tar.gz | tar zxv && \

README.md

@@ -47,7 +47,7 @@ You need to use the `docker info` command to check your docker version and use i
      singularityware/docker2singularity:1.11 \            
      ubuntu:14.04
 
-Currently only the 1.10, 1.11 and 1.12 versions are supported. If you are using an older version of Docker you will need to upgrade.
+Currently only the 1.10, 1.11, 1.12, and 1.13  versions are supported. If you are using an older version of Docker you will need to upgrade.
 
 ## Acknowledgements
 This work is heavily based on the `docker2singularity` work done by [vsoch](https://github.com/vsoch) and [gmkurtzer](https://github.com/gmkurtzer). Hopefully most of the conversion code will be merged into Singularity in the future making this container even leaner!