Update requirement on cryptography (#575)

Author: jpadilla

setup.cfg

@@ -44,15 +44,15 @@ docs =
     sphinx-rtd-theme
     zope.interface
 crypto =
-    cryptography>=2.6,<4.0.0
+    cryptography>=3.3.1,<4.0.0
 tests =
     pytest>=6.0.0,<7.0.0
     coverage[toml]==5.0.4
 dev =
     sphinx
     sphinx-rtd-theme
     zope.interface
-    cryptography>=2.6,<4.0.0
+    cryptography>=3.3.1,<4.0.0
     pytest>=6.0.0,<7.0.0
     coverage[toml]==5.0.4
     mypy