Update notes with 5.0.6 notes and 1672 fix

To be squashed.

Author: fredericDelaporte

releasenotes.txt

@@ -6,6 +6,7 @@ Release notes - NHibernate - Version 5.1.2
 ** Bug
 
    * #1680 RowCount not working with JoinEntityAlias
+   * #1672 Generated async methods do not correctly propagate OperationCanceledException
    * #1667 Collection initializing with zero rows after update to NH5
    * #1660 Wrong CopyTo implementation
    * #1650 Cannot use cache.use_sliding_expiration in hibernate.cfg.xml
@@ -222,8 +223,12 @@ Build 5.0.6
 Release notes - NHibernate - Version 5.0.6
 
 ** Bug
+    * #1672 Generated async methods do not correctly propagate OperationCanceledException
     * #1355 NH-3928 - Random invalid SQL generated when using bitwise operators
 
+** Task
+    * #1686 Release 5.0.6
+
 Build 5.0.5
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