add whats new

Author: glemaitre

doc/whats_new/v0.6.rst

@@ -31,6 +31,9 @@ Maintenance
  :class:`sklearn.utils._testing.SkipTest`.
  :pr:`617` by :user:`Guillaume Lemaitre <glemaitre>`.
 
+- Synchronize :mod:`imblearn.pipeline` with :mod:`sklearn.pipeline`.
+ :pr:`617` by :user:`Guillaume Lemaitre <glemaitre>`.
+
 Deprecation
 ...........