Update pytest requirement from <5.4 to <6.3

Updates the requirements on [pytest](https://github.com/pytest-dev/pytest) to permit the latest version.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@1.0.0b3...6.2.2)

Signed-off-by: dependabot[bot] <support@github.com>

setup.py

@@ -34,7 +34,7 @@
     extras_require={
         "test": [
             "coverage==4.5.4",
-            "pytest<5.4",
+            "pytest<6.3",
             "pytest-cov",
             "coveralls",
             "testfixtures",