dogpile.cache: add missing dep

pkgs/development/python-modules/dogpile.cache/default.nix

@@ -1,5 +1,5 @@
 { stdenv, buildPythonPackage, fetchPypi
-, pytest, pytestcov, mock, Mako, decorator
+, pytest, pytestcov, mock, Mako, decorator, stevedore
 }:
 
 buildPythonPackage rec {
@@ -26,7 +26,7 @@ buildPythonPackage rec {
 
   checkInputs = [ pytest pytestcov mock Mako ];
 
-  propagatedBuildInputs = [ decorator ];
+  propagatedBuildInputs = [ decorator stevedore ];
 
   meta = with stdenv.lib; {
     description = "A caching front-end based on the Dogpile lock";