title: Unable to install php7.1-bcmath on ubuntu 16.04
body: <p>When I run the following command : <code>composer require sonata-project/notification-bundle</code>  I have this error:</p>
  
  <pre><code>- php-amqplib/php-amqplib v2.7.2 requires ext-bcmath * -&gt; the requested PHP extension bcmath is missing from your system.
      - php-amqplib/php-amqplib v2.7.1 requires ext-bcmath * -&gt; the requested PHP extension bcmath is missing from your system.
      - php-amqplib/php-amqplib v2.7.0 requires ext-bcmath * -&gt; the requested PHP extension bcmath is missing from your system.
      - sonata-project/notification-bundle 3.4.0 requires enqueue/amqp-lib ^0.8 -&gt; satisfiable by enqueue/amqp-lib[0.8.0, 0.8.10, 0.8.11, 0.8.12, 0.8.13, 0.8.15, 0.8.2, 0.8.21, 0.8.23, 0.8.4, 0.8.5, 0.8.9].
  </code></pre>
  
  <p>Apparently bcmath is missing so I have run this:</p>
  
  <pre><code>sudo apt-get install php7.1-bcmath
  </code></pre>
  
  <p>And I get the error below:</p>
  
  <pre><code>E: Unable to locate package php7.1-bcmath
  E: Couldn't find any package by glob 'php7.1-bcmath'
  E: Couldn't find any package by regex 'php7.1-bcmath'
  </code></pre>
  
  <p>Any idea what causing the problem ? </p>
  
  <p>Symfony 4
  php 7.1
  Ubuntu 16.04</p>