Fix broken unit tests due to strict Serializable interface restrictions

[tianshuang]

Because java.util.Map and java.util.Set do not implement the Serializable interface, but 99d689c imposes strict restrictions.

[codecov-commenter]

Codecov Report

Merging #60 (e24501b) into master (b8d2a8e) will increase coverage by 0.08%.
The diff coverage is 75.00%.

@@             Coverage Diff              @@
##             master      #60      +/-   ##
============================================
+ Coverage     27.77%   27.85%   +0.08%     
- Complexity      561      566       +5     
============================================
  Files            93       93              
  Lines          6485     6487       +2     
  Branches       1077     1078       +1     
============================================
+ Hits           1801     1807       +6     
+ Misses         4449     4445       -4     
  Partials        235      235              

Impacted Files	Coverage Δ
...ibaba/com/caucho/hessian/io/SerializerFactory.java	69.56% <75.00%> (+1.21%)	⬆️
...a/com/caucho/hessian/io/AbstractHessianOutput.java	33.33% <0.00%> (+3.33%)	⬆️

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