please rewrite your composer.json.

・・・
    "repositories": [
            {
                "type": "vcs",
                "url": "https://github.com/maccotsan/CarbonJp.git"
            }
        ],
        "require": {
            "maccotsan/carbonjp": "dev-master"
        }
・・・

use maccotsan\Carbon\CarbonJp;
CarbonJp::parse("1989-01-08T12:00:00+09:00(JST)")->eraName; // => '平成'
CarbonJp::parse("1989-01-08T12:00:00+09:00(JST)")->eraNameShort; // => 'H'
CarbonJp::parse("1989-01-08T12:00:00+09:00(JST)")->yearJp; // => 1
CarbonJp::parse("1989-01-08T12:00:00+09:00(JST)")->yearJpGan; // => '元'
CarbonJp::parse("1989-01-08T12:00:00+09:00(JST)")->dayOfWeekJp; // => '日'
CarbonJp::parse("1989-01-08T12:00:00+09:00(JST)")->ampmJp; // => '午後'

CarbonJp::parse("2016-09-02T15:03:08+09:00(JST)")->format("JK年m月d日(x) Eh時i分s秒"); // => '平成28年09月02日(金) 午後03時03分08秒'

https://maccotsan.github.io/CarbonJp/

composer install --dev
composer test