Fix travis

This branch is focused on fixing the broken Travis build that we have since build [640](https://travis-ci.org/mezuro/mezuro/builds/23620030) (actually, we can't know exactly because we had the problem with Gist and Rubygems and we had some builds that simple failed to download install.sh/random gems). The problem is pretty simple: Analizo released a new version (1.17.0/1.18.0) and *deleted* the old download link (http://analizo.org/download/analizo_1.16.0_all.deb). Since ```install.sh``` didn't use ```set -e```, the ```wget``` error passed silently and nobody saw the ```error 404``` from ```wget```.

So I [forked](https://gist.github.com/m45t3r/0c4ad3b5700c6364abf1) the ```install.sh``` script, use bash ```set -eu; set -o pipefail``` (this is probably the most important change of this branch, since we detected an error early on the build instead of later) to make bash exit with non-zero in case of error and updated Analizo version to 1.18.0.

This is not the best way to do this since we already add the Analizo repository, so we should install analizo from this repository. But Travis use Ubuntu 12.04. Analizo on repository depends on some packages that only exists on Debian 7/Ubuntu 13.10+. What is even more strange is that we depend on a package that exists on Analizo repository (doxygen), so the ```install.sh``` script does add the Analizo repository to install this package(???).

So while the last version of this script should fix the Travis build, we should discuss a better way to handle this Analizo dependency. The best way would be to convince Travis to update to Ubuntu 14.04 or change to Debian 7, but I don't think they would do this for us :sweat: .

Finally, commit 01ae243 includes a refactored version of ```.travis.yml``` file. I used ```popd/pushd``` commands for a more robust change directory, using git repository instead of the RAW files from Gist (we can, of course, set a specific branch if this is needed) and removed a ```chmod``` since we can simple call the script directly with ```bash``` command.