Add dotnet sdk version to global.json (#708)

Author: Kapil Borle

global.json

@@ -1,3 +1,9 @@
 {
-    "projects": ["Engine", "Rules"]
-}
+    "projects": [
+        "Engine",
+        "Rules"
+    ],
+    "sdk": {
+        "version": "1.0.0-preview2-1-003177"
+    }
+}