fix:nacos client_test bug

[amudong]

fix:nacos client_test bug

[zouyx]

format config_center/nacos/client_test.go then make travis succes

[codecov-io]

Codecov Report

Merging #363 into develop will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #363      +/-   ##
===========================================
- Coverage    66.74%   66.72%   -0.03%     
===========================================
  Files          150      150              
  Lines         7936     7963      +27     
===========================================
+ Hits          5297     5313      +16     
- Misses        2137     2146       +9     
- Partials       502      504       +2

Impacted Files	Coverage Δ
protocol/dubbo/dubbo_invoker.go	82.25% <0%> (-7.11%)	⬇️
cluster/cluster_impl/failback_cluster_invoker.go	78.49% <0%> (-2.16%)	⬇️
registry/directory/directory.go	82.69% <0%> (-0.87%)	⬇️
remoting/zookeeper/listener.go	52.57% <0%> (+0.54%)	⬆️

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[zouyx]

Travis still failing @amudong

[AlexStocks]

LGTM