Merge pull request keras-team#538 from jfsantos/patch-2

Recent update broke HDF5Matrix

Author: fchollet

keras/utils/io_utils.py

@@ -5,8 +5,7 @@
 
 
 class HDF5Matrix():
-    def __init__(self):
-        self.refs = defaultdict(int)
+    refs = defaultdict(int)
 
     def __init__(self, datapath, dataset, start, end, normalizer=None):
         if datapath not in list(self.refs.keys()):