use const instead of strings

Author: jjw24

Plugins/Flow.Launcher.Plugin.Program/Settings.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.IO;
 
@@ -14,11 +14,13 @@ public class Settings
         public bool EnableStartMenuSource { get; set; } = true;
 
         public bool EnableRegistrySource { get; set; } = true;
-        public string CustomizedExploere { get; set; } = "exploere";
+        public string CustomizedExplorer { get; set; } = Explorer;
         public string CustomizedArgs { get; set; } = "";
 
         internal const char SuffixSeperator = ';';
 
+        internal const string Explorer = "explorer";
+
         /// <summary>
         /// Contains user added folder location contents as well as all user disabled applications
         /// </summary>