Require pyflakes<2.2.0 (fix #782) (#784)

Author: leszekpi

setup.py

@@ -52,7 +52,7 @@
             'mccabe',
             'pycodestyle',
             'pydocstyle>=2.0.0',
-            'pyflakes>=1.6.0',
+            'pyflakes>=1.6.0,<2.2.0',
             'pylint',
             'rope>=0.10.5',
             'yapf',
@@ -62,7 +62,7 @@
         'mccabe': ['mccabe'],
         'pycodestyle': ['pycodestyle'],
         'pydocstyle': ['pydocstyle>=2.0.0'],
-        'pyflakes': ['pyflakes>=1.6.0'],
+        'pyflakes': ['pyflakes>=1.6.0,<2.2.0'],
         'pylint': ['pylint'],
         'rope': ['rope>0.10.5'],
         'yapf': ['yapf'],