Do not import versionitem_seq and versionhistory_seq because they…

… are different between v5 and v7 because the v5 doesn't use this tables to store versions so that sequences are like empty. (#158)

src/pump/_sequences.py

@@ -35,6 +35,9 @@ def migrate(self, env, db7, db5_dspace, db5_utilities):
             if dspace5_seq_name not in db7_seqs_names:
                 continue
 
+            if dspace5_seq_name in ["versionhistory_seq", "versionitem_seq"]:
+                continue
+
             # use cursor according to database to which sequence belongs
             if dspace5_seq_db == "clarin-dspace":
                 db = db5_dspace