[AIRFLOW-XXX] Purge coveralls

(cherry picked from commit 33b3f6dc631a3f028efd190671bfaf6a55ce9463)
Signed-off-by: Bolke de Bruin <bolke@xs4all.nl>
(cherry picked from commit 1b53882a7cc64358e09eed3afb53069c1fba2b94)
Signed-off-by: Bolke de Bruin <bolke@xs4all.nl>
diff --git a/tox.ini b/tox.ini
index 9f36ff2..f9552de 100644
--- a/tox.ini
+++ b/tox.ini
@@ -67,4 +67,3 @@
   {toxinidir}/scripts/ci/load_data.sh
   {toxinidir}/scripts/ci/run_tests.sh []
   {toxinidir}/scripts/ci/check-license.sh
-  coveralls