add changelog for a new nuget minor version bump (Azure#17131)

Author: DorothySun216

sdk/servicebus/Microsoft.Azure.ServiceBus/CHANGELOG.md

@@ -1,6 +1,9 @@
 # Release History
 ## 5.1.0-beta.1 (Unreleased)
 
+## 5.1.0 (2020-11-20)
+- Bugfix - Fixing a bug in management client that is sending atom xml elements out of order [PR 16488](https://github.com/Azure/azure-sdk-for-net/pull/16488)
+- Bugfix - Convert "Invalid operation while connection is closing" to retriable ServiceBusException [PR 17023](https://github.com/Azure/azure-sdk-for-net/pull/17023)
 
 ## 5.0.0 (2020-09-11)
 ### Breaking Changes

sdk/servicebus/Microsoft.Azure.ServiceBus/src/Microsoft.Azure.ServiceBus.csproj

@@ -2,8 +2,7 @@
   <PropertyGroup>
     <AssemblyTitle>Azure ServiceBus SDK</AssemblyTitle>
     <Description>This is the next generation Azure Service Bus .NET Standard client library that focuses on queues &amp; topics. For more information about Service Bus, see https://azure.microsoft.com/en-us/services/service-bus/</Description>
-    <Version>5.1.0-beta.1</Version>
-    <ApiCompatVersion>5.0.0</ApiCompatVersion>
+    <Version>5.1.0</Version>
     <PackageTags>Microsoft;Azure;Service Bus;ServiceBus;.NET;AMQP;IoT;Queue;Topic</PackageTags>
     <TargetFrameworks>$(RequiredTargetFrameworks)</TargetFrameworks>
     <NoWarn>$(NoWarn);CS1591;CS1573;NU5125</NoWarn>