test: add read_only_space heap space

v8.getHeapSpaceStatistics() now includes read_only_space
in its results. Update test-v8-stats.js to account for this.

Fixes: nodejs/node-v8#44

PR-URL: #19989
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Myles Borins <myles.borins@gmail.com>

test/parallel/test-v8-stats.js

@@ -25,7 +25,8 @@ const expectedHeapSpaces = [
   'old_space',
   'code_space',
   'map_space',
-  'large_object_space'
+  'large_object_space',
+  'read_only_space'
 ];
 const heapSpaceStatistics = v8.getHeapSpaceStatistics();
 const actualHeapSpaceNames = heapSpaceStatistics.map((s) => s.space_name);