Fixed bug caused with accessing request.bodyFields when Content type is application/json

[Dammyololade]

Description

This PR is a fix for #https://github.com/syedmurtaza108/chucker-flutter/issues/6 which was caused by accessing request.bodyfields. Accessing bodyFields on request with content type other than application/x-www-form-urlencoded throws a state error. I hereby provided a fix for that with encoding the result of request.body

With this PR, it's ensured that request body with any content type can be accessed without throwing any error.

Type of Change

• [ ] ✨ New feature (non-breaking change which adds functionality)
• [ x] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [ ] 📝 Documentation
• [ ] 🗑️ Chore

[codecov-commenter]

Codecov Report

Merging #7 (010af7d) into master (0d6fd28) will decrease coverage by 0.19%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master       #7      +/-   ##
==========================================
- Coverage   84.25%   84.05%   -0.20%     
==========================================
  Files          36       36              
  Lines        1264     1267       +3     
==========================================
  Hits         1065     1065              
- Misses        199      202       +3     

Impacted Files	Coverage Δ
lib/src/http/chucker_http_client.dart	85.71% <0.00%> (-6.60%)	:arrow_down:

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