Merge pull request #7 from matplotlib/travis

Update .travis.yml

Author: story645

.travis.yml

@@ -19,6 +19,7 @@ matrix:
 install:
   - python -m pip install --upgrade pip
   - python -m pip install --upgrade codecov coverage pytest
+  - python -m pip install -r test_requirements.txt
   - python -m pip install -ve .
 
 script:

test_requirements.txt

@@ -0,0 +1 @@
+vega-datasets>=0.5.0