Update types.h

Author: LamentXU123

Include/internal/mimalloc/mimalloc/types.h

@@ -705,7 +705,7 @@ void _mi_stat_counter_increase(mi_stat_counter_t* stat, size_t amount);
 // Thread Local data
 // ------------------------------------------------------
 
-// A "span" is is an available range of slices. The span queues keep
+// A "span" is an available range of slices. The span queues keep
 // track of slice spans of at most the given `slice_count` (but more than the previous size class).
 typedef struct mi_span_queue_s {
   mi_slice_t* first;