updated requirements

.travis.yml

@@ -6,7 +6,7 @@ script:
   - coverage run -m unittest discover # - python -m unittest discover if we don't need coverage
   - pylint --disable=R,C addme/
 install:
-  - pip install pandas  # e.g. see https://github.com/pallets/jinja/blob/master/.travis.yml
+  - pip install -r requirements.txt  # see https://stackoverflow.com/questions/14399534/reference-requirements-txt-for-the-install-requires-kwarg-in-setuptools-setup-py
   - pip install codecov
   - pip install coverage
   - pip install pylint

setup.py

@@ -1,5 +1,6 @@
 from setuptools import setup
 
+# see https://stackoverflow.com/questions/14399534/reference-requirements-txt-for-the-install-requires-kwarg-in-setuptools-setup-py
 setup(name='addme',
       version='0.1',
       description='Add two numbers using the pandas Series sum method',