pin pytest-cov to fix failing build

Derwent · Derwent · commit dd4374ca8005 · 2019-05-05T12:05:20.000+10:00
see: pywbem/pywbem#1371
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
