Fix filtered search manager spec teaspoon error

spec/javascripts/filtered_search/filtered_search_manager_spec.js.es6

@@ -23,6 +23,7 @@
         `);
         spyOn(gl.FilteredSearchManager.prototype, 'bindEvents').and.callFake(() => {});
+        spyOn(gl.FilteredSearchManager.prototype, 'cleanup').and.callFake(() => {});
         spyOn(gl.FilteredSearchManager.prototype, 'loadSearchParamsFromURL').and.callFake(() => {});
         spyOn(gl.FilteredSearchDropdownManager.prototype, 'setDropdown').and.callFake(() => {});
         spyOn(gl.utils, 'getParameterByName').and.returnValue(null);