update pypy on tox (#402)

* update pypy on tox

* update

Author: auvipy

tox.ini

@@ -22,7 +22,7 @@ commands =
     integration: py.test -xv -E rabbitmq t/integration {posargs:-n2}
 basepython =
     flake8,apicheck,linkcheck,pydocstyle: python3.8
-    pypy3: pypy
+    pypy3: pypy3.9
     3.7: python3.7
     3.8: python3.8
     3.9: python3.9