fix: clients should be Record<string ,ClusterOptions>

[JerrysShan]

在使用ts的过程中，发现配置文件这个编译时报错，发现index.d.ts文件中clients类型有问题。

[codecov[bot]]

Codecov Report

Merging #31 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #31   +/-   ##
=======================================
  Coverage   84.09%   84.09%           
=======================================
  Files           4        4           
  Lines          44       44           
=======================================
  Hits           37       37           
  Misses          7        7

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