[skip ci] Fix some spelling (#9605)

Signed-off-by: Nmin.tian <min.tian.cn@gmail.com>

docs/design_docs/datanode_flowgraph_recovery_design_0604_2021.md

@@ -24,7 +24,7 @@ When a flowgraph flushes a segment, we need to save these things:
 - all other segments' current positions from replica (If a segment hasn't been flushed, save the position when datanode first meets it.)
 
 Whether save successfully:
-- If successed, flowgraph updates all segments' positions to replica
+- If succeeded, flowgraph updates all segments' positions to replica
 - If not
     - For a grpc failure( this failure will appear after many times retry internally), crush itself.
     - For a normal failure, retry save 10 times, if fail still, crush itself.