raft: remove duplicate letter in comment.
raft: remove duplicate letter in comment.

Signed-off-by: 1ab5d54bc728e67a16fc49877054b331401e6740@qq.com
Signed-off-by: 王霄霄 <6870d88be32ca17c8f6c7affdf0dcc21d1d826cf@qq.com>

etcd-io/etcd,etcd-io/etcd,etcd-io/etcd