Update Travis CI config file to use py.test.

.travis.yml

@@ -1,12 +1,10 @@
 language: python
 python:
+  - "2.6"
   - "2.7"
+  - "pypy"
 install:
   - pip install -r requirements.txt
+  - pip install pytest
 script:
-  - sh run_tests -x
-#notifications:
-#  irc:
-#    channels: "irc.freenode.org#sentry"
-#    on_success: change
-#    on_failure: change
+  - py.test