Rename License.md

For strict compliance with the requirements in https://docs.opensource.microsoft.com/releasing/ rename LICENSE.md to LICENSE.txt. The license file doesn't make any use of Markdown formatting, anyway.

Author: tmeschter

LICENSE.md LICENSE.txt

@@ -67,7 +67,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "items", "items", "{5204CAC5
 		Directory.Build.targets = Directory.Build.targets
 		Directory.Packages.props = Directory.Packages.props
 		Launch.cmd = Launch.cmd
-		LICENSE.md = LICENSE.md
+		LICENSE.txt = LICENSE.txt
 		nuget.config = nuget.config
 		README.md = README.md
 		SECURITY.md = SECURITY.md