DOC correct PR number of last commit

Author: glemaitre

doc/whats_new/v0.7.rst

@@ -74,7 +74,7 @@ Enhancements
 - Add option `output_dict` in
   :func:`imblearn.metrics.classification_report_imbalanced` to return a
   dictionary instead of a string.
-  :pr:`xx` by :user:`Guillaume Lemaitre <glemaitre>`.
+  :pr:`770` by :user:`Guillaume Lemaitre <glemaitre>`.
 
 Deprecation
 ...........