Fix c-lightning configure not finding python

Broke in the latest release.

site-cookbooks/kosmos-bitcoin/recipes/c-lightning.rb

@@ -28,6 +28,7 @@ bash "compile_c-lightning" do
     make
     make install
   EOH
+  environment "PYTHON_VERSION" => "3"
   action :nothing
   notifies :restart, "systemd_unit[lightningd.service]", :delayed
 end