title: Composer two packages conflicting on dependency version
body: <p>I already have the <a href="https://packagist.org/packages/geoip2/geoip2" rel="nofollow">geoip2</a> package installed. When I installed it some time ago, it required guzzle 3.* so it installed guzzle 3.9.1 as one of its dependencies.</p>
  
  <p>Now I want to install the <a href="https://packagist.org/packages/predictionio/predictionio" rel="nofollow">predicitonio</a> package, so I added it to my composer.json</p>
  
  <pre><code>"require": {
      ...
      ...
      "geoip2/geoip2": "0.6.*",
      "predictionio/predictionio": "~0.7.1"
  }
  </code></pre>
  
  <p>The issue is <a href="https://packagist.org/packages/predictionio/predictionio" rel="nofollow">predictionio</a> requires guzzle 3.8.0 or 3.8.1, it won't accept the already installed 3.9.1 version.</p>
  
  <p>I believe <a href="https://packagist.org/packages/guzzle/guzzle" rel="nofollow">guzzle</a> 3.8.0 would satisfy both <a href="https://packagist.org/packages/geoip2/geoip2" rel="nofollow">geoip2</a> and <a href="https://packagist.org/packages/predictionio/predictionio" rel="nofollow">predictionio</a>, so the question is how can I downgrade <a href="https://packagist.org/packages/guzzle/guzzle" rel="nofollow">guzzle</a>, keeping in mind <a href="https://packagist.org/packages/guzzle/guzzle" rel="nofollow">guzzle</a> doesn't appear in my composer.json, only the composer.lock.</p>
  
  <p>Below is the output when I run <code>composer update predictionio/predictionio</code></p>
  
  <pre><code>  Problem 1
      - Installation request for predictionio/predictionio ~0.7.1 -&gt; satisfiable by predictionio/predictionio[v0.7.1].
      - Conclusion: remove guzzle/guzzle v3.9.1
      - predictionio/predictionio v0.7.1 requires guzzle/guzzle ~3.8.0 -&gt; satisfiable by guzzle/guzzle[v3.8.0, v3.8.1].
      - Can only install one of: guzzle/guzzle[v3.9.1, v3.8.0].
      - Can only install one of: guzzle/guzzle[v3.9.1, v3.8.1].
      - Installation request for guzzle/guzzle == 3.9.1.0 -&gt; satisfiable by guzzle/guzzle[v3.9.1].
  </code></pre>