Upgrade Julia to v0.5

This is pretty hacky -- we're using a Ubuntu 14.04 PPA to install
something on Debian Jessie -- but everything seems to work.

datascience-notebook/Dockerfile

@@ -15,7 +15,9 @@ RUN apt-get update && \
     rm -rf /var/lib/apt/lists/*
 
 # Julia dependencies
-RUN apt-get update && \
+RUN echo "deb http://ppa.launchpad.net/staticfloat/juliareleases/ubuntu trusty main" > /etc/apt/sources.list.d/julia.list && \
+    apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3D3D3ACC && \
+    apt-get update && \
     apt-get install -y --no-install-recommends \
     julia \
     libnettle4 && apt-get clean && \

datascience-notebook/README.md

@@ -9,7 +9,7 @@
 * pandas, matplotlib, scipy, seaborn, scikit-learn, scikit-image, sympy, cython, patsy, statsmodel, cloudpickle, dill, numba, bokeh pre-installed
 * Conda R v3.3.x and channel
 * plyr, devtools, dplyr, ggplot2, tidyr, shiny, rmarkdown, forecast, stringr, rsqlite, reshape2, nycflights13, caret, rcurl, and randomforest pre-installed
-* Julia v0.3.x with Gadfly, RDatasets and HDF5 pre-installed
+* Julia v0.5.x with Gadfly, RDatasets and HDF5 pre-installed
 * Unprivileged user `jovyan` (uid=1000, configurable, see options) in group `users` (gid=100) with ownership over `/home/jovyan` and `/opt/conda`
 * [tini](https://github.com/krallin/tini) as the container entrypoint and [start-notebook.sh](../base-notebook/start-notebook.sh) as the default command
 * A [start-singleuser.sh](../base-notebook/start-singleuser.sh) script useful for running a single-user instance of the Notebook server, as required by JupyterHub