Fix codecov (coverage not installed outside of tox) (#424)

* codecov: rename config file

Docs say that it needs to be named `codecov.yml`, or specified via
argument to codecov-bash.

* ci: Travis: pip install coverage

This got lost when `scrutinizer-ocular`.

Author: blueyed

.travis.yml

@@ -30,6 +30,7 @@ script:
 after_script:
   - if [ $CI_TARGET = tests ]; then
       set -x;
+      pip install coverage;
       coverage combine;
       coverage report -m;
       coverage xml;