fix build

The build currently fails until I separate numpy to install 1st.
I see something like this has already happened and solved the same with pandas/statsmodels.
The --upgrade suppresses one of the warnings, not sure if it works without or not, I think it fails due to version dependency. 
good points.  sounds good.
in practice i barely saw barely/no difference though.
see:
```diff
diff --git a/Dockerfile b/Dockerfile
index 62e59fb..3b4a7a7 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,22 +4,25 @@ MAINTAINER Dieter Plaetinck <dieter@vimeo.com>
 # /var/dump for redis data
 RUN mkdir -p /var/log/skyline /var/run/skyline /var/log/redis /var/dump/
 
-RUN apt-get update
 # python-dev is for numpy
-RUN apt-get install -y python-setuptools python-scipy git python-dev
+# wget gcc build-essential is for redis
+
+RUN apt-get update && \
+    apt-get install -y python-setuptools python-scipy git python-dev wget gcc build-essential && \
+    apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 RUN easy_install pip
 
 #Redis
-RUN apt-get install -y wget gcc build-essential
-RUN wget http://download.redis.io/releases/redis-2.6.16.tar.gz
-RUN tar --extract --gzip --directory /opt --file redis-2.6.16.tar.gz
-RUN cd /opt/redis-2.6.16 && make
+RUN wget http://download.redis.io/releases/redis-2.6.16.tar.gz && \
+    tar --extract --gzip --directory /opt --file redis-2.6.16.tar.gz && \
+    rm redis-2.6.16.tar.gz && \
+    cd /opt/redis-2.6.16 && make
 
 ENV PATH $PATH:/opt/redis-2.6.16/src
 
-RUN pip install --upgrade numpy 
-RUN pip install pandas patsy msgpack-python
-RUN pip install statsmodels  # must install pandas first :/
+RUN pip install --upgrade numpy && \
+    pip install pandas patsy msgpack-python && \
+    pip install statsmodels  # must install pandas first :/
 
 RUN git clone https://github.com/etsy/skyline.git /opt/skyline
 
@@ -30,7 +33,5 @@ RUN chmod +x /usr/bin/skyline-start.sh
 
 ADD skyline-settings.py /opt/skyline/src/settings.py
 
-RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
-
 ENV PATH $PATH:/opt/skyline/bin
 CMD ["skyline-start.sh"]
```
the saved image went from 585M to 575M :'(