Revert name of LICENSE file, update link in README.md

Author: jeanmarc

LICENSE.md renamed to LICENSE

@@ -255,7 +255,7 @@ Output:
 If you have any ideas, [open an issue](https://github.com/plantuml-stdlib/Archimate-PlantUML/issues/new) or fork the repository and submit a pull request.
 
 ## License
-This project is licensed under the MIT License - see the [LICENSE.md](LICENSE.md) file for details
+This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details
 
 ## Acknowledgments
 * [PlantUML Reference Guide](http://plantuml.com/PlantUML_Language_Reference_Guide.pdf) - PlantUML Reference Guide