Added bio unit fix to CHANGELOG

CHANGELOG.txt

@@ -6,6 +6,8 @@ Changes In Release 1.3.2
   * Fix atom indices generated by CoordGroup::Filter()
   * small tweaks to lDDT output
   * small tweaks to molck
+  * Repaired bio unit parsing from mmCIF file/ PDBizing bio units, before
+    chains with different transformations were ignored
 
 Changes In Release 1.3.1
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