Fatal error: Class 'Spyc' not found in Config.php

[theasteve]

I'm currently working with PHP version 7.1.7 on OS High Sierra. It seems Spyc is not able to read the variables in the config.yml file. Following the documentation I been trying to set the API Key for Google Analytics. This is what my composer.json file looks like:

{
  "name": "nyco/wp-config",
  "version": "0.0.5",
  "type": "wordpress-muplugin",
  "license": "GPL-3.0+",
  "description": "A WordPress package for environment configuration.",
  "homepage": "https://github.com/cityofnewyork/nyco-wp-config",
  "authors": [
    {
      "name": "Devon Hirth",
      "email": "dehirth@nycopportunity.nyc.gov",
      "homepage": "https://github.com/devowhippit"
    }
  ],
  "keywords": [
    "wordpress",
    "environment",
    "configuration"
  ],
  "support": {
    "issues": "https://github.com/cityofnewyork/nyco-wp-config/issues"
  },
  "require": {
    "composer/installers": "~1.0",
    "mustangostang/spyc": "^0.6.2",
    "illuminate/encryption": "^5.6"
  },
  "require-dev": {
    "squizlabs/php_codesniffer": "3.*",
    "codeception/codeception": "^2.3"
  },
  "scripts": {
    "lint": [
      "vendor/bin/phpcs --standard=standard.xml --extensions=php --ignore=vendor/ ."
    ],
    "fix": [
      "vendor/bin/phpcbf --standard=standard.xml --extensions=php --ignore=vendor/ ."
    ]
  }
}

I created the file mu-plugins/mu-autoloader.php as stated in the documentation of wp-config

The plugin comes in a directory, so you will need to create an mu-plugin autoloader to get it to be used by your WordPress installation

mu-plugins/mu-autoloader.php

namespace MustUsePlugins;

const PLUGINS = [
  '/wp-config/Config.php',
];

for ($i=0; $i < sizeof(PLUGINS); $i++) {
  if (file_exists(WPMU_PLUGIN_DIR . PLUGINS[$i]))
    require WPMU_PLUGIN_DIR . PLUGINS[$i];
}

When I browsed to localhost:8000 it shows the following error message:

Fatal error: Class 'Spyc' not found in /var/www/html/wp-content/mu-plugins/wp-config/Config.php on line 37

Which is produced in the following line:

if (file_exists($path . 'config.yml')) {
  $config = Spyc::YAMLLoad($path . 'config.yml');

When I remove mu-autoloader.php file I'm able to load the page on the browser but without the environment being read by the following template:

{% if function('getenv', 'GOOGLE_ANALYTICS') != '' %}
  <script async src='https://www.googletagmanager.com/gtag/js?id={{ function('getenv', 'GOOGLE_ANALYTICS') }}'></script>
  <script>
    window.dataLayer = window.dataLayer || [];
    function gtag(){dataLayer.push(arguments);}
    gtag('js', new Date());
    gtag('config', "{{ function('getenv', 'GOOGLE_ANALYTICS') }}");
  </script>
{% endif  %}