Initialize Files

Initialize Files to reduce needless setup to create a gist.

Octokit.Tests/Clients/GistsClientTests.cs

@@ -33,10 +33,7 @@ public class GistsClientTests
             newGist.Description = "my new gist";
             newGist.Public = true;
 
-            var gistFiles = new Dictionary<string, string>();
-            gistFiles.Add("myGistTestFile.cs", "new GistsClient(connection).Create();");
-
-            newGist.Files = gistFiles;
+            newGist.Files.Add("myGistTestFile.cs", "new GistsClient(connection).Create();");
             
             client.Create(newGist);
 

Octokit/Models/Request/NewGist.cs

@@ -1,9 +1,15 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
+
 namespace Octokit
 {
     public class NewGist
     {
+        public NewGist()
+        {
+            Files = new Dictionary<string, string>();
+        }
+
         /// <summary>
         /// The description of the gist.
         /// </summary>