title: Why does composer complain about the ext-mongo extension?
body: <p>When I try to install doctrine/mongodb-odm-bundle and doctrine/mongodb with composer it throws an error.</p>
  
  <pre class="lang-sh prettyprint-override"><code>composer require doctrine/mongodb-odm-bundle doctrine/mongodb
  </code></pre>
  
  <pre class="lang-sh prettyprint-override"><code>Using version ^3.5 for doctrine/mongodb-odm-bundle
  Using version ^1.6 for doctrine/mongodb
  ./composer.json has been updated
  Loading composer repositories with package information
  Updating dependencies (including require-dev)
  Your requirements could not be resolved to an installable set of packages.
  
    Problem 1
      - doctrine/mongodb 1.6.3 requires ext-mongo ^1.6.7 -&gt; the requested PHP extension mongo is missing from your system.
      - doctrine/mongodb 1.6.2 requires ext-mongo ^1.6.7 -&gt; the requested PHP extension mongo is missing from your system.
      - doctrine/mongodb 1.6.1 requires ext-mongo ^1.6.7 -&gt; the requested PHP extension mongo is missing from your system.
      - doctrine/mongodb 1.6.0 requires ext-mongo ^1.6.7 -&gt; the requested PHP extension mongo is missing from your system.
      - Installation request for doctrine/mongodb ^1.6 -&gt; satisfiable by doctrine/mongodb[1.6.0, 1.6.1, 1.6.2, 1.6.3].
  
    To enable extensions, verify that they are enabled in your .ini files:
      - 
      - /usr/local/etc/php/conf.d/docker-php-ext-mongodb.ini
      - /usr/local/etc/php/conf.d/docker-php-ext-pdo_mysql.ini
      - /usr/local/etc/php/conf.d/docker-php-ext-soap.ini
      - /usr/local/etc/php/conf.d/docker-php-ext-sodium.ini
      - /usr/local/etc/php/conf.d/docker-php-ext-zip.ini
    You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.
  
  Installation failed, reverting ./composer.json to its original content.
  
  </code></pre>
  
  <p>I was suprised to see this error message because I did install Mongodb with pecl and enabled it with an ini file.</p>
  
  <pre><code>RUN pecl install mongodb \
      &amp;&amp; docker-php-ext-enable mongodb
  </code></pre>
  
  <p>Does anyone knows how to solve this?</p>