fixes #730

[GavinChenYan]

set the discovery result to serviceMap cache

[codecov-commenter]

Codecov Report

Merging #731 into 1.6.x will increase coverage by 0.02%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##              1.6.x     #731      +/-   ##
============================================
+ Coverage     49.87%   49.89%   +0.02%     
- Complexity     1923     1926       +3     
============================================
  Files           261      261              
  Lines         11756    11757       +1     
  Branches       1670     1671       +1     
============================================
+ Hits           5863     5866       +3     
+ Misses         5198     5196       -2     
  Partials        695      695              

Impacted Files	Coverage Δ	Complexity Δ
.../main/java/com/networknt/cluster/LightCluster.java	53.84% <0.00%> (-1.06%)	7.00 <0.00> (ø)
.../src/main/java/com/networknt/client/oauth/Jwt.java	71.92% <0.00%> (+1.75%)	18.00% <0.00%> (+1.00%)
.../src/main/java/com/networknt/utility/HashUtil.java	63.33% <0.00%> (+3.33%)	11.00% <0.00%> (+1.00%)

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