fixing sha512 call

common/python/nomadcore/json_support.py

 import json
+from nomadcore.compact_sha import sha512
+
 """Various functions to simplify and standardize dumping objects to json"""
 
 class ExtraIndenter(object):
@@ -95,7 +97,7 @@ class ShaStreamer(object):
     def __init__(self, shas = None):
         self.shas = shas
         if shas is None:
-            self.shas = (CompactSha.sha224(),)
+            self.shas = (sha512(),)
     def write(self, val):
         for sha in self.shas:
             sha.update(val)