update pytest-cov requirements to fix CI build

Derwent · Derwent · commit 1326d89d965e · 2019-05-05T12:14:48.000+10:00
diff --git a/requirements-test.txt b/requirements-test.txt
@@ -1,6 +1,6 @@
 -r requirements.txt
 httmock
 pytest
-pytest-cov
+pytest-cov<2.6.0
 coverage
 codecov
