Add missing RuntimeException class
bug #112 Add missing RuntimeException class (willdurand)

This PR was merged into the master branch.

Discussion
----------

Add missing RuntimeException class

Got the following fatal error while running Sismo on a (restricted) web server:

    Fatal error: Class 'Symfony\Component\Process\Exception\RuntimeException' not found in /home/willdurand/ci/sismo.php on line 167

Commits
-------

37d282f Add missing RuntimeException class