Bump macOS incremental rollout flag to 5%. (duckduckgo#1238)

Author: samsymons

overrides/macos-override.json

@@ -9,6 +9,9 @@
                         "steps": [
                             {
                                 "percent": 1.0
+                            },
+                            {
+                                "percent": 5.0
                             }
                         ]
                     }