tox: use wheels instead of sdist

Author: dcrosta

tox.ini

@@ -27,6 +27,8 @@ deps =
     flask11:   flask>=1.1,<1.2
     flask2x:   flask>=2.0,<3.0
 
+package = wheel
+wheel_build_env = .pkg
 commands =
     {envbindir}/py.test --tb=native {toxinidir}