Update Images.json (#18654)

Author: eugeneogongo

src/Compute/Compute/Strategies/ComputeRp/Images.json

@@ -39,7 +39,7 @@
                   "UbuntuLTS":  {
                                     "publisher":  "Canonical",
                                     "offer":  "UbuntuServer",
-                                    "sku":  "16.04-LTS",
+                                    "sku":  "20.04-LTS",
                                     "version":  "latest"
                                 }
               },