Fix Pytest4.x compatibility error

According to pytest docs:

```
[pytest] section in setup.cfg files

Removed in version 4.0.

[pytest] sections in setup.cfg files should now be named [tool:pytest] to
avoid conflicts with other distutils commands.
```

Signed-off-by: Stanislav Levin <[email protected]>

Author: stanislavlevin

setup.cfg

@@ -1,6 +1,6 @@
 [bdist_wheel]
 universal=1
 
-[pytest]
+[tool:pytest]
 testpaths = tests
 norecursedirs = .git tmp* .eggs bin build include lib share src