Fix tox

Author: saimn

tox.ini

@@ -6,7 +6,7 @@ requires =
     virtualenv >= 20
 
 [testenv]
-extra = tests
+extras = tests
 commands=
     python --version
     pip --version
@@ -18,6 +18,6 @@ usedevelop = True
 whitelist_externals = sphinx-build
 passenv = HOME
 deps =
-extra = docs
+extras = docs
 commands =
     sphinx-build docs docs/_build/html