update changelog

Author: rcannood

CHANGELOG.md

@@ -239,4 +239,6 @@
   and thus can't be directly overriden (new values given by get_donor_batch_map is int) (PR #119).
 
 * Update flowsom mapping similarity so we subset to just markers to correct, and lisi to remove control samples
-  and unlabelled cells (PR #119).
+  and unlabelled cells (PR #119).
+* Fix bug in `average_batch_r2` where the R2 was computed on all cell types of a donor at once
+  instead of on each cell type separately (PR #127).