update version

Author: reneeli@microsoft.com

src/aks-preview/HISTORY.rst

@@ -16,6 +16,10 @@ Pending
 * Add aks extension and aks extension-type command groups
 * Remove TrustedAccess commands from aks-preview extension as it is GA and exists in azure-cli for long time.
 
+15.0.0b2
+++++++++
+* Add option `--migrate-vmas-to-vms` to `az aks update`
+
 15.0.0b1
 ++++++++
 * [BREAKING CHANGE] Change `--vm-sizes` for VirtualMachines manual profile to awalys support single SKU size.
@@ -27,7 +31,6 @@ Pending
 14.0.0b6
 +++++++
 * Add option `--acns-advanced-networkpolicies <None|FQDN|L7>` to `az aks create/update`
-* Add option `--migrate-vmas-to-vms` to `az aks update`
 
 14.0.0b5
 ++++++++