tox.ini: configure coveralls

tox.ini

@@ -20,6 +20,20 @@ commands =
     # run the test suite
     py.test
 
+[testenv:coveralls]
+passenv = TRAVIS TRAVIS_JOB_ID TRAVIS_BRANCH
+basepython=python3.5
+deps =
+    {[testenv]deps}
+    pytest-cov
+    coveralls
+skip_install = true
+ignore_outcome = true
+commands=
+    # measure test coverage and upload report to coveralls
+    py.test --cov
+    coveralls
+
 [pytest]
 minversion = 2.8
 testpaths =