changed lru_cache to be functools not methodtools version

bilby/core/prior/dict.py

@@ -3,7 +3,7 @@ from io import open as ioopen
 import json
 import numpy as np
 import os
-from methodtools import lru_cache
+from functools import lru_cache
 
 from future.utils import iteritems
 from matplotlib.cbook import flatten