adds missing else clause (facebook#10660)

Author: NikaBuligini

scripts/tasks/flow.js

@@ -19,8 +19,10 @@ spawn(path.join('node_modules', '.bin', 'flow' + extension), ['check', '.'], {
   stdio: 'inherit',
 }).on('close', function(code) {
   if (code !== 0) {
-    console.log('Flow failed');
+    console.error('Flow failed');
+  } else {
+    console.log('Flow passed');
   }
-  console.log('Flow passed');
+
   process.exit(code);
 });