Updated docker PWD part of the command (#1235)

Author: eddiebergman

doc/installation.rst

@@ -169,7 +169,7 @@ To start a Jupyter notebook, you could instead run e.g.:
 
 .. code:: bash
 
-    docker run -it -v $PWD:/opt/nb -p 8888:8888 mfeurer/auto-sklearn:master /bin/bash -c "mkdir -p /opt/nb && jupyter notebook --notebook-dir=/opt/nb --ip='0.0.0.0' --port=8888 --no-browser --allow-root"
+    docker run -it -v ${PWD}:/opt/nb -p 8888:8888 mfeurer/auto-sklearn:master /bin/bash -c "mkdir -p /opt/nb && jupyter notebook --notebook-dir=/opt/nb --ip='0.0.0.0' --port=8888 --no-browser --allow-root"
 
 Alternatively, it is possible to use the development version of auto-sklearn by replacing all
 occurences of ``master`` by ``development``.