fix a typo in r28862. this bug was found by failures of testERP5DocumentSyncML.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@29088 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/Document.py

@@ -239,7 +239,7 @@ class ConversionCacheMixin:
     """Update md5 checksum from the original file
     """
     data = self.getData()
-    self._setContentMd5(md5.new(data).digest()) #reindex is useless
+    self._setContentMd5(md5.new(data).hexdigest()) #reindex is useless
 
 class PermanentURLMixIn(ExtensibleTraversableMixIn):
   """