title: Yarn installing multiple versions of the same package
body: <p>I have <code>angular</code> in my dependencies at 1.5.11:</p>
  
  <pre><code>{
      "dependencies": {
          "angular": "1.5.11",
          "angular-foundation": "0.7.0"
      }
  }
  </code></pre>
  
  <p><code>angular-foundation</code> happens to depend on <code>angular@&gt;=1.3.0</code>.</p>
  
  <p>Why does Yarn install <code>angular@1.6.9</code> as a nested dependency of angular-foundation instead of using the project's version? This causes angular to exist twice in the app and doesn't work properly:</p>
  
  <p><code>node_modules
    angular (1.5.11)
    angular-foundation (0.7.0)
      node_modules
        angular (1.6.9)
  </code></p>
  
  <p>This doesn't happen with npm@5.6.0 - npm uses 1.5.11 for both the app and the package.</p>