Using ujson to load ticker files from disk during backtest

is over 30% faster.

freqtrade/optimize/__init__.py

@@ -164,7 +164,7 @@ def load_cached_data_for_updating(filename: str,
     # read the cached file
     if os.path.isfile(filename):
         with open(filename, "rt") as file:
-            data = ujson.load(file)
+            data = json.load(file)
             # remove the last item, because we are not sure if it is correct
             # it could be fetched when the candle was incompleted
             if data: