Update Black version.

.github/CONTRIBUTING.md

@@ -33,7 +33,7 @@ Install the project in editable mode:
 pip install -e .
 ```
 
-Install formatter, linter and test system: `pip install black~=21.4b0 flake8 mypy pytest pytest-cov`.
+Install formatter, linter and test system: `pip install black flake8 mypy pytest pytest-cov`.
 
 Be sure to enable Git hooks:
 

.github/workflows/test.yml

@@ -18,7 +18,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install black~=21.4b0 flake8 pytest
+        pip install black flake8 pytest
         pip install -r requirements.txt
         pip install .
     - name: Check code style with Black
@@ -41,7 +41,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install black~=21.4b0 flake8 pytest
+        pip install black flake8 pytest
         pip install -r requirements.txt
         pip install .
     - name: Check code style with Black

doc/contributing.moi

@@ -30,7 +30,7 @@ Install the project in editable mode:
 
 \code {pip install -e .} {shell}
 
-Install formatter, linter and test system\: \m {pip install black~=21.4b0 flake8 mypy pytest pytest-cov}.
+Install formatter, linter and test system\: \m {pip install black flake8 mypy pytest pytest-cov}.
 
 Be sure to enable Git hooks: