Re-enable unit test as server issue is resolved.

Author: PGijsbers

tests/test_tasks/test_task_functions.py

@@ -84,8 +84,6 @@ def test_list_tasks_empty(self):
 
         self.assertIsInstance(tasks, dict)
 
-    @unittest.skip("Server will currently incorrectly return only 99 tasks."
-                   "See https://github.com/openml/OpenML/issues/980")
     def test_list_tasks_by_tag(self):
         num_basic_tasks = 100  # number is flexible, check server if fails
         tasks = openml.tasks.list_tasks(tag='OpenML100')