TST: Limit the timer report to just the 15 longest tests

The default of all the tests is pretty spammy.

.travis.yml

@@ -28,6 +28,6 @@ before_script:
   - pip freeze | sort
   - "flake8 zipline tests"
 script:
-  - nosetests --with-timer --exclude=^test_examples --with-coverage --cover-package=zipline
+  - nosetests --with-timer --exclude=^test_examples --with-coverage --cover-package=zipline --timer-top-n=15
 after_success:
   - coveralls

setup.cfg

@@ -3,6 +3,7 @@ verbosity=2
 detailed-errors=1
 with-ignore-docstrings=1
 with-timer=1
+timer-top-n=15
 
 [metadata]
 description-file = README.rst