update class attribute access modifier

Update class attribute access modifier from private to protected for class Response

add default value null for parameter `errorCode`

Merge pull request #5 from harryosmar/json-encode

add parameter `$errorCode` null

use trait set content type

Merge pull request #4 from harryosmar/json-encode

add json encode method

Fix composer.json

Merge pull request #3 from harryosmar/fix-composer-json

fix invalid `type` composer.json

add parameter errorCode

Merge pull request #2 from harryosmar/add-error-code

Add error code

v1.0.4

update readme

update readme

v1.0.3

update readme

Update test coverage

v1.0.2

fix bug test set status code duplication

Update readme

v1.0.1

update readme

First Release

v1.0.0

update readme broken url