增加sentinel报错 ERR unknown command 'SENTINEL'

版本：
version = 2018-11-04 16:22:35 +0800 @de1ad026e329561c22e2a3035fbfe89dc7fef764 @3.2.2-12-gde1ad02
compile = 2018-12-11 15:22:54 +0800 by go version go1.8.5 linux/amd64

[root@10-8-16-143 codis]# ./bin/codis-admin --dashboard=10.8.16.143:18080 --sentinel-add --addr=10.8.16.143:26379
错误信息：
2018/12/11 18:19:23 dashboard.go:646: [PANIC] call rpc add-sentinel to dashboard 10.8.16.143:18080 failed
[error]: [Remote Error] ERR unknown command 'SENTINEL'
6 /opt/gopath/src/github.com/CodisLabs/codis/pkg/utils/redis/client.go:74
github.com/CodisLabs/codis/pkg/utils/redis.(*Client).Do
5 /opt/gopath/src/github.com/CodisLabs/codis/pkg/utils/redis/sentinel.go:784
github.com/CodisLabs/codis/pkg/utils/redis.(*Sentinel).FlushConfig.func1
4 /opt/gopath/src/github.com/CodisLabs/codis/pkg/utils/redis/sentinel.go:84
github.com/CodisLabs/codis/pkg/utils/redis.(*Sentinel).do
3 /opt/gopath/src/github.com/CodisLabs/codis/pkg/utils/redis/sentinel.go:789
github.com/CodisLabs/codis/pkg/utils/redis.(*Sentinel).FlushConfig
2 /opt/gopath/src/github.com/CodisLabs/codis/pkg/topom/topom_sentinel.go:37
github.com/CodisLabs/codis/pkg/topom.(*Topom).AddSentinel
1 /opt/gopath/src/github.com/CodisLabs/codis/pkg/topom/topom_api.go:470
github.com/CodisLabs/codis/pkg/topom.(*apiServer).AddSentinel
0 /opt/gopath/src/github.com/CodisLabs/codis/pkg/topom/topom_api.go:117
github.com/CodisLabs/codis/pkg/topom.(*apiServer).AddSentinel-fm
... ...
[stack]:
2 /opt/gopath/src/github.com/CodisLabs/codis/cmd/admin/dashboard.go:646
main.(*cmdDashboard).handleSentinelCommand
1 /opt/gopath/src/github.com/CodisLabs/codis/cmd/admin/dashboard.go:76
main.(*cmdDashboard).Main
0 /opt/gopath/src/github.com/CodisLabs/codis/cmd/admin/main.go:82
main.main
... ...