rephrase comment (#16559)

Author: jamesgeorge007

packages/react-dom/src/server/ReactThreadIDAllocator.js

@@ -8,7 +8,7 @@
  */
 
 // Allocates a new index for each request. Tries to stay as compact as possible so that these
-// indices can be used to reference a tightly packaged array. As opposed to being used in a Map.
+// indices can be used to reference a tightly packed array. As opposed to being used in a Map.
 // The first allocated index is 1.
 
 import invariant from 'shared/invariant';