Satisfy CI: The coverage package asked for TOML support

The error message was:

    Can't read 'pyproject.toml' without TOML support.
    Install with [toml] extra

Author: amotl

setup.cfg

@@ -76,7 +76,7 @@ install_requires =
 test =
     parameterized>=0.8,<1
     codecov>=2.1.0
-    coverage>=5.2.0
+    coverage[toml]>=5.2.0
     unittest-xml-reporting>=3.0.0
     requests-mock>=1.8.0