Merge pull request #3 from longaccess/zip64pack

when writing zip64 header pack format must be bytes

Author: allanlei

zipstream/__init__.py

@@ -116,7 +116,7 @@ def FileHeader(self, zip64=None):
         if zip64 is None:
             zip64 = file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT
         if zip64:
-            fmt = '<HHQQ'
+            fmt = b'<HHQQ'
             extra = extra + struct.pack(fmt,
                     1, struct.calcsize(fmt)-4, file_size, compress_size)
         if file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT: