updated .travis; Travis wouldn't run 'py.tests'...suggested 'py.test'

Author: sommersoft

.travis.yml

@@ -26,7 +26,7 @@ install:
   - pip install pylint circuitpython-build-tools Sphinx sphinx-rtd-theme pytest
 
 script:
-  - py.tests
+  - py.test
   - pylint adafruit_motor/*.py
   - ([[ ! -d "examples" ]] || pylint --disable=missing-docstring,invalid-name examples/*.py)
   - ([[ ! -d "tests" ]] || pylint --disable=missing-docstring tests/*.py)