Pin a Python dependency

Author: mdmintz

requirements.txt

@@ -135,6 +135,7 @@ pytest-cov==3.0.0;python_version>="3.6"
 flake8==3.7.9;python_version<"3.5"
 flake8==3.9.2;python_version>="3.5" and python_version<"3.6"
 flake8==4.0.1;python_version>="3.6"
+mccabe==0.6.1
 pyflakes==2.1.1;python_version<"3.5"
 pyflakes==2.3.1;python_version>="3.5" and python_version<"3.6"
 pyflakes==2.4.0;python_version>="3.6"

setup.py

@@ -263,6 +263,7 @@
             'flake8==3.7.9;python_version<"3.5"',
             'flake8==3.9.2;python_version>="3.5" and python_version<"3.6"',
             'flake8==4.0.1;python_version>="3.6"',
+            'mccabe==0.6.1',
             'pyflakes==2.1.1;python_version<"3.5"',
             'pyflakes==2.3.1;python_version>="3.5" and python_version<"3.6"',
             'pyflakes==2.4.0;python_version>="3.6"',