Fix CFBundleVersion

Summary:
This defaults to the `version` and is used to update the inline plists
of the Frameworks that are bundled with the MacOS app bundle. Setting
them to a fixed value means that they remain unchanged across rebuilds
(bringing them in line with Linux and Windows equivalents). This
is required to ship them as separate bundles for the launcher.

Why 50? The reason this was introduced was to allow people to override
this to values >= 50 as this is somehow a Mac App Store requirement:
electron-userland/electron-builder#565 (comment)

Reviewed By: priteshrnandgaonkar

Differential Revision: D21179072

fbshipit-source-id: a6f10b7508526b4305b229bd160d6e570ddce822

desktop/scripts/build-release.ts

@@ -115,6 +115,9 @@ async function buildDist(buildFolder: string) {
         linux: {
           executableName: 'flipper',
         },
+        mac: {
+          bundleVersion: '50.0.0',
+        },
       },
       projectDir: buildFolder,
       targets,