Update db.py

In python3.X, we need to convert map object to list, to be able serialize it.

Issue #431

Author: w-diesel

debug_toolbar/utils/tracking/db.py

@@ -98,7 +98,7 @@ def execute(self, sql, params=()):
                 stacktrace = []
             _params = ''
             try:
-                _params = json.dumps(map(self._decode, params))
+                _params = json.dumps(list(map(self._decode, params)))
             except Exception:
                 pass  # object not JSON serializable