Add references

Author: jjw24

Flow.Launcher.Core/Plugin/PluginsLoader.cs

@@ -4,8 +4,9 @@
 using System.Linq;
 using System.Reflection;
 using System.Runtime.Loader;
+using System.Threading.Tasks;
+using System.Windows;
 using Flow.Launcher.Infrastructure;
-using Flow.Launcher.Infrastructure.Exception;
 using Flow.Launcher.Infrastructure.Logger;
 using Flow.Launcher.Infrastructure.UserSettings;
 using Flow.Launcher.Plugin;