Update CI.yml

Changed to build on 2019 server to support .Net Framework 4.6.1

Author: ShawnLaMountain

.github/workflows/CI.yml

@@ -14,7 +14,7 @@ env:
 jobs:
   build:
 
-    runs-on: [windows-latest]
+    runs-on: [windows-2019]
 
     steps:
     - name: Checkout