Set black to >=19.3b0,<20 (#296)

Author: fabaff

setup.py

@@ -94,7 +94,7 @@ def get_git_commit_datetime() -> str:
 
 # Should be as close to Home Assistant dev/master as possible
 TESTS_REQUIRE = [
-    "black==19.3b0;python_version>'3.6'",
+    "black>=19.3b0,<20;python_version>'3.6'",
     'coveralls==1.2.0',
     'flake8-docstrings==1.3.0',
     'flake8==3.7.7',