Use super for SimpleDatabase operations

Closes https://github.com/decentral1se/xbotlib/issues/5.

test_xbotlib.py

@@ -101,3 +101,10 @@ def test_config(config):
     assert config.serve
     assert config.storage == "file"
     assert config.output == "."
+
+
+def test_simple_message_delete(tmp_db_path):
+    db = SimpleDatabase(tmp_db_path, log)
+    db["foo"] = "bar"
+    del db["foo"]
+    assert "foo" not in db

xbotlib.py

@@ -59,12 +59,12 @@ class SimpleDatabase(dict):
 
     def __setitem__(self, key, val):
         """Write data to the database."""
-        dict.__setitem__(self, key, val)
+        super().__setitem__(key, val)
         self._dumps()
 
     def __delitem__(self, key):
         """Remove data from the database."""
-        dict.__delitem__(key)
+        super().__delitem__(key)
         self._dumps()
 
     def update(self, *args, **kwargs):