update changelog

CHANGELOG.md

@@ -1,10 +1,11 @@
 <a name="v0.3.1"></a>
-## v0.3.1 (Unreleased)
+## v0.3.1 (27/06/2024)
 
 * Every iterator can now retrieve indices of other iterators.
 * Prod iterators have now a method to fetch a tuple of mutable slices; useful to directly
   write data without the need to use copy or clone methods.
 * A convenience method to busy-wait for a certain amount of items has been added.
+* Fixed a bug that could cause indices to overlap.
 
 <a name="v0.3.0"></a>
 ## v0.3.0 (13/05/2024)