Update Microsoft.Toolkit.Uwp.Notifications.nuspec

Author: michael-hawker

Microsoft.Toolkit.Uwp.Notifications/Microsoft.Toolkit.Uwp.Notifications.nuspec

@@ -8,7 +8,7 @@
     <requireLicenseAcceptance>true</requireLicenseAcceptance>
     <license type="expression">MIT</license>
     <projectUrl>https://github.com/windows-toolkit/WindowsCommunityToolkit</projectUrl>
-    <iconUrl>https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/build/nuget.png</iconUrl>
+    <iconUrl>https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/main/build/nuget.png</iconUrl>
     <icon>images\nuget.png</icon>
     <description>The official way to send toast notifications on Windows 10 via code rather than XML, with the help of IntelliSense. Supports all C# app types, including WPF, UWP, WinForms, and Console, even without packaging your app as MSIX. Also supports C++ UWP apps.