fix license link in sln (#4555)

Author: SimonCropp

Source/csla.build.sln

@@ -9,10 +9,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 		Directory.Build.props = Directory.Build.props
 		Directory.Package.props = Directory.Package.props
 		global.json = global.json
-		..\license.txt = ..\license.txt
 		..\README.md = ..\README.md
 		..\releasenotes.md = ..\releasenotes.md
 		version.json = version.json
+		..\license.md = ..\license.md
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Core", "Core", "{85799E16-9B3B-4BD5-98D6-238E31291134}"