Correct the readme

Author: nedbat

README.rst

@@ -20,8 +20,8 @@ library to determine which lines are executable, and which have been executed.
 Coverage.py runs on many versions of Python:
 
 * CPython 2.7.
-* CPython 3.5 through 3.9 alpha 3.
-* PyPy2 7.0 and PyPy3 7.0.
+* CPython 3.5 through 3.9 alpha 4.
+* PyPy2 7.3.0 and PyPy3 7.3.0.
 
 Documentation is on `Read the Docs`_.  Code repository and issue tracker are on
 `GitHub`_.