ceph: Fix wrapper path

pkgs/tools/filesystems/ceph/generic.nix

···
   wrapArgs = "--set PYTHONPATH \"$(toPythonPath $lib)\""
     + " --prefix PYTHONPATH : \"$(toPythonPath ${python.modules.readline})\""
     + " --prefix PYTHONPATH : \"$(toPythonPath ${pythonPackages.flask})\""
-    + " --set PATH : \"$out/bin\"";
+    + " --set PATH \"$out/bin\"";
 in
 stdenv.mkDerivation {
   name="ceph-${version}";