Add missing --enable-ext to udocker test. (#1019)

Author: tetron

tests/test_udocker.py

@@ -58,7 +58,7 @@ def test_udocker_usage_should_not_write_cid_file(self, tmpdir):
     def test_udocker_should_display_memory_usage(self, tmpdir):
         cwd = tmpdir.chdir()
         error_code, stdout, stderr = get_main_output(
-            ["--default-container=debian",  "--user-space-docker-cmd=" + self.udocker_path,
+            ["--enable-ext", "--default-container=debian",  "--user-space-docker-cmd=" + self.udocker_path,
              get_data("tests/wf/timelimit.cwl"), "--sleep_time", "10"])
         cwd.chdir()
         tmpdir.remove(ignore_errors=True)