Pinning coverage version due to magical reasons.

Aaron Loo · Aaron Loo · commit 3810f0bb7f9e · 2020-03-27T12:50:58.000-07:00
For more information, see Yelp/py_zipkin#139.
diff --git a/requirements-dev.txt b/requirements-dev.txt
@@ -1,4 +1,6 @@
-coverage
+# coveragepy==5.0 fails with `Safety level may not be changed inside a transaction
+# on python 3.6.0 (xenial)
+coverage<5
 flake8==3.5.0
 mock
 monotonic
