Restore SDK 5.0 in global.json and have AppVeyor overwrite the file

appveyor.yml

@@ -34,3 +34,5 @@ build_script:
 
 
     rem appveyor UpdateBuild -Version %BUILDFILE%
+install:
+- ps: Set-Content -Path global.json -Value '{"sdk":{"version":"3.1.100","rollForward":"latestFeature"}}'

global.json

@@ -1,6 +1,6 @@
 {
 	"sdk": {
-		"version": "3.1.100",
+		"version": "5.0.100",
-		"rollForward": "latestMajor"
+		"rollForward": "latestFeature"
 	}
 }