Update Dockerfile

Latest master removed the `--system` flag. You can pass a `--user` flag for non-system install.

Dockerfile

@@ -1,66 +1,66 b''
 # Installs IPython from the current branch
 # Another Docker container should build from this one to get services like the notebook
 
 FROM ubuntu:14.04
 
 MAINTAINER IPython Project <[e-mail]>
 
 ENV DEBIAN_FRONTEND noninteractive
 
 # Not essential, but wise to set the lang
 # Note: Users with other languages should set this in their derivative image
 RUN apt-get update && apt-get install -y language-pack-en
 ENV LANGUAGE en_US.UTF-8
 ENV LANG en_US.UTF-8
 ENV LC_ALL en_US.UTF-8
 
 RUN locale-gen en_US.UTF-8
 RUN dpkg-reconfigure locales
 
 # Python binary dependencies, developer tools
 RUN apt-get update && apt-get install -y -q \
     build-essential \
     make \
     gcc \
     zlib1g-dev \
     git \
     python \
     python-dev \
     python-pip \
     python3-dev \
     python3-pip \
     python-sphinx \
     python3-sphinx \
     libzmq3-dev \
     sqlite3 \
     libsqlite3-dev \
     pandoc \
     libcurl4-openssl-dev \
     nodejs \
     nodejs-legacy \
     npm
 
 # In order to build from source, need less
 RUN npm install -g less@1.7.5
 
 RUN pip install invoke
 
 RUN mkdir -p /srv/
 WORKDIR /srv/
 ADD . /srv/ipython
 WORKDIR /srv/ipython/
 RUN chmod -R +rX /srv/ipython
 
 # .[all] only works with -e, so use file://path#egg
 # Can't use -e because ipython2 and ipython3 will clobber each other
 RUN pip2 install file:///srv/ipython#egg=ipython[all]
 RUN pip3 install file:///srv/ipython#egg=ipython[all]
 
 # install kernels
-RUN python2 -m IPython kernelspec install-self --system
-RUN python3 -m IPython kernelspec install-self --system
+RUN python2 -m IPython kernelspec install-self
+RUN python3 -m IPython kernelspec install-self
 
 WORKDIR /tmp/
 
 RUN iptest2
 RUN iptest3