update LICENSE.txt (making the MIT license detectable)

LICENSE.txt

-==============================================
-This is a copy of the MIT license.
-==============================================
-Copyright (C) 2012-2017 Mort Yao <mort.yao@gmail.com>
-Copyright (C) 2012 Boyu Guo <iambus@gmail.com>
+MIT License
 
-Permission is hereby granted, free of charge, to any person obtaining a copy of
-this software and associated documentation files (the "Software"), to deal in
-the Software without restriction, including without limitation the rights to
-use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
-of the Software, and to permit persons to whom the Software is furnished to do
-so, subject to the following conditions:
+Copyright (c) 2012-2019 Mort Yao <mort.yao@gmail.com>
+Copyright (c) 2012 Boyu Guo <iambus@gmail.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in all
 copies or substantial portions of the Software.