Update docs.

Build/MQTTnet.nuspec

@@ -12,6 +12,7 @@
     <requireLicenseAcceptance>true</requireLicenseAcceptance>
     <description>MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker) and supports v3.1.0, v3.1.1 and v5.0.0 of the MQTT protocol.</description>
     <releaseNotes>
+* [Core] Added .NET 5.0 TFMs (thanks to @StefanOssendorf, @JanEggers).
 * [Core] Added support for TLS 1.3 (requires .NET Core 3.1+) (thanks to @Dvergatal).
 * [Core] Added support for _MaximumQoS_ transmit when using MQTTv5 (thanks to @nayato).
 * [Core] Aligned the format of some log messages.
@@ -24,7 +25,7 @@
 * [Server] Improved message processing performance (+ ~5%).
 * [Server] Fix wrong usage of client session items for undelivered messages.
 
-Git commit: $gitCommit
+      Git commit: $gitCommit
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2020</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin Blazor</tags> 

Source/MQTTnet.Server/Web/Startup.cs

@@ -186,8 +186,7 @@ namespace MQTTnet.Server.Web
 
             var webSocketOptions = new WebSocketOptions
             {
-                KeepAliveInterval = TimeSpan.FromSeconds(mqttSettings.WebSocketEndPoint.KeepAliveInterval),
-                ReceiveBufferSize = mqttSettings.WebSocketEndPoint.ReceiveBufferSize
+                KeepAliveInterval = TimeSpan.FromSeconds(mqttSettings.WebSocketEndPoint.KeepAliveInterval)
             };
 
             if (mqttSettings.WebSocketEndPoint.AllowedOrigins?.Any() == true)