[Bug] Return valid Json when executing programs

[nathanhopp]

🐛 Bug Report

Improve outputs when executing program commands

Steps to Reproduce

curl <host>/<network>/program/credits.aleo/mapping/bonded/<public_key> 
"{\n  validator: <public_key>,\n  microcredits: 21091223930u64\n}"

The above can't be parsed, and is not valid json.

Expected Behavior

It should return valid json, example:

{
  "validator": "<public_key>",
  "microcredits": "21065418248u64"
}

Even better microcredits not having u64.

Your Environment

independent of env.