Update Dockerfile.

Fixed to not use `apt-get upgrade` &
`apt-get update` is not on a single line
re: dockerfile best practices
https://docs.docker.com/articles/dockerfile_best-practices/

Signed-off-by: Jessica Frazelle <[e-mail]>

Dockerfile

@@ -7,13 +7,9 b' MAINTAINER IPython Project <[e-mail]>'
 
 ENV DEBIAN_FRONTEND noninteractive
 
-# Make sure apt is up to date
-RUN apt-get update
-RUN apt-get upgrade -y
-
 # Not essential, but wise to set the lang
 # Note: Users with other languages should set this in their derivative image
-RUN apt-get install -y language-pack-en
+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
@@ -22,14 +18,31 b' RUN locale-gen en_US.UTF-8'
 RUN dpkg-reconfigure locales
 
 # Python binary dependencies, developer tools
-RUN apt-get install -y -q build-essential make gcc zlib1g-dev git && \
-    apt-get install -y -q python python-dev python-pip python3-dev python3-pip && \
-    apt-get install -y -q libzmq3-dev sqlite3 libsqlite3-dev pandoc libcurl4-openssl-dev nodejs nodejs-legacy npm
+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
 
-RUN apt-get install -y -q python-sphinx python3-sphinx
 RUN pip install invoke
 
 RUN mkdir -p /srv/