fix(travis): increase ulimit
fix(travis): increase ulimit

Now that performance tests are run, it appears we run into one
particular failure on travis, possibly indicating a bug in python 3.3.

Just bluntly increason the amount of handles might silence it... .

Related to #524

nvie/GitPython,gitpython-developers/GitPython,breavo/GitPython,jeblair/GitPython,gitpython-developers/GitPython,gitpython-developers/gitpython,breavo/GitPython,jeblair/GitPython,nvie/GitPython,gitpython-developers/gitpython