Fix node +x bit in server distribution

Summary: This was lost when I changed from `pkg-fetch` writing it to copying the file.

Reviewed By: mweststrate, aigoncharov

Differential Revision: D36682861

fbshipit-source-id: 23822d4cc75720a83282de949d28029a05a2a7f9

desktop/scripts/build-flipper-server-release.tsx

@@ -391,6 +391,8 @@ async function installNodeBinary(outputPath: string, platform: BuildPlatform) {
     nodeRange: SUPPORTED_NODE_PLATFORM,
   });
   await fs.copyFile(path, outputPath);
+  // Set +x on the binary as copyFile doesn't maintain the bit.
+  await fs.chmod(outputPath, 0o755);
 }
 
 async function setUpMacBundle(