title: Ignore tests folder when send to packagist
body: <p>I have a project with the following structure:</p>
  
  <pre><code>- src
  ----/ /* Relevant files */
  - tests
  ----/ /* Irrelevant files */
  - composer.json
  - phpunit.xml
  </code></pre>
  
  <p>The project is sent to packagist on every commit already. But, it is sending the test files.</p>
  
  <p>I'd like to ignore <code>tests</code> folder, so composer wont download unecessary files when someone calls <code>composer require my/package</code></p>
  
  <p>Here is whats the content of my composer.json looks like:</p>
  
  <pre><code>{
      "name": "my/package",
      "description": "...",
      "type": "library",
      "license": "MIT",
      "require": {
          "php": "&gt;=7"
      },
      "require-dev": {
          "phpunit/phpunit": "&gt;=5.4"
      },
      "autoload": {
          "psr-4": {
              "MyProject\\": "./src"
          }
      }
  }
  </code></pre>