Change code coverage provider to codecov

Author: takluyver

.travis.yml

@@ -10,9 +10,9 @@ before_install:
 
 install:
     - pip install -U setuptools
-    - pip install -f travis-wheels/wheelhouse -e .[test] coveralls
+    - pip install -f travis-wheels/wheelhouse -e .[test] codecov
     - python -c 'import ipykernel.kernelspec; ipykernel.kernelspec.install(user=True)'
 script:
     - nosetests --with-coverage --cover-package jupyter_client jupyter_client
 after_success:
-    - coveralls
+    - codecov