Fix wheel-making

Author: nedbat

tox_wheels.ini

@@ -2,15 +2,15 @@
 # For details: https://github.com/nedbat/coveragepy/blob/master/NOTICE.txt
 
 [tox]
-envlist = py{27,35,36,37,38,sys}
+envlist = py{27,35,36,37,38,39,sys}
 toxworkdir = {toxinidir}/.tox/wheels
 
 [testenv]
 deps =
     -rrequirements/wheel.pip
 
 commands =
-    python -c "import sys; print(sys.real_prefix)"
+    python -c "import sys; print(sys.base_prefix)"
     python setup.py bdist_wheel {posargs}
 
 [testenv:py27]