Added before install prerequisite for travis

Author: pkittenis

.travis.yml

@@ -3,6 +3,8 @@ python:
   - "2.5"
   - "2.6"
   - "2.7"
+before_install:
+  - sudo apt-get install -qq libevent-dev
 install:
   - pip install -r requirements.txt --use-mirrors
 script: nosetests