Removed utf8bom

* https://github.com/dwango/UniVRM/pull/27
* https://msdn.microsoft.com/ja-jp/library/ms143375(v=vs.110).aspx
* File.WriteAllText(path, str, Encoding.UTF8) is with BOM
* File.WriteAllText(path, str) default encoding is without BOM

Scripts/SpringBone/VRMSpringUtility.cs

@@ -56,7 +56,7 @@ namespace VRM
                 spring.boneGroups.Add
                 );
 
-            File.WriteAllText(path, spring.ToJson(), Encoding.UTF8);
+            File.WriteAllText(path, spring.ToJson());
         }
 
         #endregion