gc.c: [DOC] fix typo

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63159 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

gc.c

@@ -1409,7 +1409,7 @@ heap_pages_expand_sorted(rb_objspace_t *objspace)
 {
     /* usually heap_allocatable_pages + heap_eden->total_pages == heap_pages_sorted_length
      * because heap_allocatable_pages contains heap_tomb->total_pages (recycle heap_tomb pages).
-     * howerver, if there are pages which do not have empty slots, then try to create new pages
+     * however, if there are pages which do not have empty slots, then try to create new pages
      * so that the additional allocatable_pages counts (heap_tomb->total_pages) are added.
      */
     size_t next_length = heap_allocatable_pages;