Update LICENSE.txt so that it's recognized as MIT (#57)

* Update LICENSE.txt so that Github recognizes it as MIT.
* Remove the term All Rights Reserved as Microsoft no longer recommend it.

See also: PowerShell/PowerShell#12729

Author: xtqqczze

LICENSE.txt

@@ -1,13 +1,9 @@
-PowerShell IoT Module
-
-Copyright (c) Microsoft Corporation. All rights reserved.
-
-All rights reserved.
+Copyright (c) Microsoft Corporation.
 
 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
+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