Make DefaultMimeTypes read-write again (fixes #302). (#303)

Author: rdeago

src/Unosquare.Labs.EmbedIO/Constants/MimeTypes.cs

@@ -1,5 +1,6 @@
 namespace Unosquare.Labs.EmbedIO.Constants
 {
+    using System.Collections.Concurrent;
     using System.Collections.Generic;
 
     /// <summary>
@@ -15,7 +16,7 @@ public static class MimeTypes
         /// on 2019-04-26.
         /// Licensed under MIT license as per https://github.com/samuelneff/MimeTypeMap/blob/master/LICENSE
         /// </remarks>
-        public static IReadOnlyDictionary<string, string> DefaultMimeTypes { get; } = new Dictionary<string, string>(Strings.StandardStringComparer)
+        public static IDictionary<string, string> DefaultMimeTypes { get; } = new ConcurrentDictionary<string, string>(new Dictionary<string, string>(Strings.StandardStringComparer)
         {
             #region Big freaking list of mime types
 
@@ -699,6 +700,6 @@ public static class MimeTypes
             {"x-world/x-vrml", ".xof"},
 
             #endregion
-        };
+        }, Strings.StandardStringComparer);
     }
 }

src/Unosquare.Labs.EmbedIO/Modules/FileModuleBase.cs

@@ -25,7 +25,7 @@ public abstract class FileModuleBase
         /// <value>
         /// The MIME type dictionary.
         /// </value>
-        public IReadOnlyDictionary<string, string> MimeTypes { get; } = Constants.MimeTypes.DefaultMimeTypes;
+        public IDictionary<string, string> MimeTypes { get; } = Constants.MimeTypes.DefaultMimeTypes;
 
         /// <summary>
         /// The default headers.