python-future missing python 3.8 and 3.9 support

[Libor Ukropec]

Hello Jon, maintainers,

who is now the maintainer of the python-future - Jon Turney?

The python-future supports only python 2.7, 3.6 and 3.7 and these are 
basically obsolete. I'd like to add support for 3.8 and 3.9 - it should 
allow me to support `duplicity` package with the latest python (3.9).

PYTHON_WHEEL_VERSIONS variable should help. Can I kindly ask someone for 
the package update?

Thank you and regards,
Libor

diff --git a/python-future.cygport b/python-future.cygport
index 3151b74..6f586ae 100644
--- a/python-future.cygport
+++ b/python-future.cygport
@@ -3,6 +3,7 @@ VERSION=0.18.2
  RELEASE=1
  ARCH=noarch

+PYTHON_WHEEL_VERSIONS="2.7:3.6:3.7:3.8:3.9"
  inherit python-wheel

  HOMEPAGE="http://python-future.org/"
@@ -20,3 +21,4 @@ src_install() {
  }

  python36_future_CONTENTS+=" usr/bin/*"
+python37_future_CONTENTS+=" usr/bin/*"