Add unittest.main() call to test_traceback.py

.travis.yml

@@ -6,8 +6,6 @@ python:
   - "3.2"
   - "3.3"
   - "3.4"
-  - pypy
-  - pypy3
 install:
  - pip install -U pip wheel setuptools
  - pip install -r requirements.txt

traceback2/tests/test_traceback.py

@@ -903,3 +903,6 @@ class TestTracebackException(unittest.TestCase):
             u('    ^\n'),
             u('SyntaxError: uh oh\n')],
             list(exc.format()))
+
+if __name__ == '__main__':
+    unittest.main()