Revert "Merge pull request #105 from tiagocardoso/fix_json_dependency"

This reverts commit 96a02d76fe65b59e239ac0b529b5b9d06c87c868, reversing
changes made to 7d9284b4a47618e756a3f443b9bcf27b12238fb9.
Revert "Merge pull request #103 from tiagocardoso/fix_json_dependency"
Switch to dart:convert for JSON to fix #104