fix option '--max-clients'

[muicoder]

before

[root@localhost redis]# ./src/redis-cluster-proxy --max-clients 10000 127.0.0.1:7000
Invalid option '--max-clients' or invalid number of option arguments

......

after

[root@localhost redis]# ./src/redis-cluster-proxy --max-clients 10000 127.0.0.1:7000
[2020-04-23 15:35:24.828/M] Redis Cluster Proxy v999.999.999 (unstable)
[2020-04-23 15:35:24.829/M] Commit: (cf40f0b4/0)
[2020-04-23 15:35:24.829/M] Git Branch: unstable
[2020-04-23 15:35:24.829/M] PID: 55016
[2020-04-23 15:35:24.829/M] OS: Linux 3.10.0-862.11.6.el7.x86_64 x86_64
[2020-04-23 15:35:24.829/M] Bits: 64
[2020-04-23 15:35:24.829/M] Log level: info
[2020-04-23 15:35:24.829/M] Connections pool size: 10 (respawn 2 every 50ms if below 10)
[2020-04-23 15:35:24.830/M] Listening on *:7777
[2020-04-23 15:35:24.830/M] Starting 8 threads...
[2020-04-23 15:35:24.830/M] Fetching cluster configuration...
[2020-04-23 15:35:24.833/M] Cluster Address: 127.0.0.1:7000
[2020-04-23 15:35:24.833/M] Cluster has 3 masters and 3 replica(s)
[2020-04-23 15:35:24.871/M] All thread(s) started!