Add missing trailing slash to the end of URL
Use package versions available in Ubuntu 12.04
Remove the -qq option (quiet mode) from apt-get install
Add support for 32-bit machines

Travis CI virtual machines are based on Ubuntu 12.04 LTS Server
Edition 64 bit, but this change allows us to test the Bash script,
without having to commit and push to GitHub, in 32-bits systems too.
Install NumPy and matplotlib using apt-get