Update docs.

Build/MQTTnet.nuspec

@@ -10,7 +10,8 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker).</description>
-    <releaseNotes>* [ManagedClient] Added max pending messages count option.
+    <releaseNotes> * [Core] Updated nuget packages due to security issues.
+* [ManagedClient] Added max pending messages count option.
 * [ManagedClient] Add pending messages overflow strategy option.
 * [Server] Added new method which exposes all retained messages.
 * [Server] Removed (wrong) setter from the server options interface.