Update black to latest version, to avoid a bug that was in 21.6b0 and 21.7b0 releases. (#1434)

Author: ashleysommer

black.toml

@@ -1,5 +1,5 @@
 [tool.black]
-required-version = "21.6b0"
+required-version = "21.9b0"
 line-length = "88"
 skip-string-normalization = true
 target-version = ['py37']

docs/developers.rst

@@ -13,7 +13,7 @@ Please be as Pythonic as possible (:pep:`8`).
 
 Code should be formatted using `black <https://github.com/psf/black>`_.
 While not yet mandatory, it will be required in the future  (6.0.0+).1
-Use Black v21.6b1, with the black.toml config file provided.
+Use Black v21.9b0, with the black.toml config file provided.
 
 Code should also pass `flake8 <https://github.com/psf/black>`_ linting
 and `mypy <http://mypy-lang.org/>`_ type checking.

requirements.dev.txt

@@ -6,7 +6,7 @@ coverage
 flake8
 doctest-ignore-unicode==0.1.2
 berkeleydb
-black==21.6b0
+black==21.9b0
 flake8-black
 mypy
 types-setuptools

setup.py

@@ -13,7 +13,7 @@
     "nose==1.3.7",
     "nose-timer",
     "coverage",
-    "black==21.6b0",
+    "black==21.9b0",
     "flake8",
     "doctest-ignore-unicode==0.1.2",
 ]