revert type of CommandServiceConfig QuotationMarkAliasMap to Dictionary

src/Discord.Net.Commands/CommandServiceConfig.cs

@@ -19,7 +19,7 @@ namespace Discord.Commands
 
         /// <summary> Collection of aliases that can wrap strings for command parsing. 
         /// represents the opening quotation mark and the value is the corresponding closing mark.</summary>
-        public IReadOnlyDictionary<char, char> QuotationMarkAliasMap { get; set; }
+        public Dictionary<char, char> QuotationMarkAliasMap { get; set; }
         = new Dictionary<char, char>()
         {
             {'\"', '\"' },