title: Why flutter version solving failed between firebase_core and firebase_messaging?
body: <p>In <strong>pubspec.yaml</strong>, if I use the following dependencies of <em>firebase_core</em> and <em>firebase_messaging</em> :</p>
  <pre class="lang-yaml prettyprint-override"><code>dependencies:
  
    firebase_core: ^0.7.0
    firebase_messaging: ^7.0.3
  </code></pre>
  <p>I get the following error message :</p>
  <pre><code>Because firebase_messaging &gt;=7.0.3 &lt;8.0.0-dev.7 depends on firebase_core ^0.5.0+1 and yourApp depends on firebase_core ^0.7.0, firebase_messaging &gt;=7.0.3 &lt;8.0.0-dev.7 is forbidden.
  So, because youApp depends on firebase_messaging ^7.0.3, version solving failed.
  pub get failed (1; So, because chat_app depends on firebase_messaging ^7.0.3, version solving failed.)
  </code></pre>