python.pkgs.wrapPython: fix permitUserSite logic

Right now the logic for `permitUserSite` is reversed: when it is set to
`false` (the default), it will add the `PYTHONNOUSERSITE=true`, while it
should be opposite. This results in all packages that use Python's wrap
to unnecessary include this environment variable.

pkgs/development/interpreters/python/wrap.sh

@@ -75,7 +75,7 @@ wrapPythonProgramsIn() {
                                     --prefix PATH ':' "$program_PATH"
                                     )
 
-                    if [ -z "$permitUserSite" ]; then
+                    if [ -n "$permitUserSite" ]; then
                         wrap_args+=(--set PYTHONNOUSERSITE "true")
                     fi