make Dockerfile work again w/o errs

I tried out the fig.yml, but this fatal error occured:
```
Err http://archive.ubuntu.com raring-security/universe amd64 Packages
  404  Not Found [IP: 91.189.91.13 80]
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/raring/main/source/Sources  404  Not Found [IP: 91.189.91.13 80]
```
which could be fixed by using the latest ubuntu and not 13.04 raring.

A minor (non-fatal) was
```
    building 'markupsafe._speedups' extension
    x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c markupsafe/_speedups.c -o build/temp.linux-x86_64-2.7/markupsafe/_speedups.o
    markupsafe/_speedups.c:12:20: fatal error: Python.h: No such file or directory
     #include <Python.h>
                        ^
    compilation terminated.
    ==========================================================================
    WARNING: The C extension could not be compiled, speedups are not enabled.
    Failure information, if any, is above.
    Retrying the build without the C extension now.
```
which can be fixed by installing the python-dev package.

BTW: The links to fig documentation in the [Blog Post](http://engineroom.trackmaven.com/blog/a-better-development-environment-with-docker-and-fig/) are 404 because fig migrated their docs to another URL without redirecting.