Enable Sandy by default if part of GK

Summary:
Inverted the condition of checking if Sandy is enabled, so by default it is enabled if user is part of the GK.

This will make it more frictionless for people joining the dogfooding group and increases the chances we receive feedback :)

Reviewed By: jknoxville

Differential Revision: D24830075

fbshipit-source-id: d20dacd9e6c2dd2387a94b8a972252f29d0dab0e

desktop/app/src/init.tsx

@@ -103,7 +103,7 @@ function init() {
     store,
     {name: 'loadTheme', fireImmediately: true, throttleMs: 500},
     (state) => ({
-      sandy: state.settingsState.enableSandy,
+      sandy: GK.get('flipper_sandy') && !state.settingsState.disableSandy,
       dark: state.settingsState.darkMode,
     }),
     (theme) => {