fix(#42): accept List<JsonObject> as possible data in Response.json

[francescovallone]

Description

The Response.json can now parse more complex objects.

Fixes #42

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 4 lines in your changes missing coverage. Please review.

Project coverage is 84.58%. Comparing base (edfb04b) to head (1e7b55c).
Report is 2 commits behind head on develop.

Files	Patch %	Lines
packages/serinus/lib/src/http/response.dart	82.35%	3 Missing ⚠️
packages/serinus/bin/serinus.dart	80.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #43      +/-   ##
===========================================
- Coverage    88.69%   84.58%   -4.11%     
===========================================
  Files           65       66       +1     
  Lines         1963     2083     +120     
===========================================
+ Hits          1741     1762      +21     
- Misses         222      321      +99     

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