Fix incorrect comment in NodeSelectorSlot javadoc

[kexianjun]

Describe what this PR does / why we need it

correct comment error

Does this pull request fix one issue?

Describe how you did it

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Special notes for reviews

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #419 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #419      +/-   ##
============================================
- Coverage     37.74%   37.73%   -0.02%     
+ Complexity      983      982       -1     
============================================
  Files           235      235              
  Lines          7407     7407              
  Branches       1014     1014              
============================================
- Hits           2796     2795       -1     
  Misses         4253     4253              
- Partials        358      359       +1

Impacted Files	Coverage Δ	Complexity Δ
.../sentinel/slots/nodeselector/NodeSelectorSlot.java	94.73% <ø> (ø)	4 <0> (ø)	⬇️
...a/com/alibaba/csp/sentinel/node/StatisticNode.java	65.57% <0%> (-1.64%)	21% <0%> (-1%)

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[sczyh30]

LGTM

[sczyh30]

Thanks!