title: Flutter not picking custom fonts based on fontWeight
body: <p>How to choose different font weights without specifying new family for each weight?</p>
  
  <pre><code>  fonts:
   - family: Montserrat
     fonts:
       - asset: assets/fonts/Montserrat-Regular.ttf
         weight: 100
       - asset: assets/fonts/Montserrat-Bold.ttf
         weight: 700
   - family: MontserratBold
     fonts:
       - asset: assets/fonts/Montserrat-Bold.ttf
  </code></pre>
  
  <p>and the widgets:</p>
  
  <pre><code>                      child: Text(
                      'TEST',
                      style: TextStyle(
                        fontSize: 17.4,
                        fontFamily: 'Montserrat',
                        fontWeight: FontWeight.w700,
                        color: Colors.black87,
                      ),
                    ),
  </code></pre>
  
  <p>.. </p>
  
  <pre><code>                      child: Text(
                      'TEST2',
                      style: TextStyle(
                          fontSize: 17.4,
                          fontFamily: 'MontserratBold',
                          color: Colors.black87),
                    ),
  </code></pre>
  
  <p>The actual Montserrat-Bold is only used with 'TEST2'. I have tried using 'Packages get' in pubspec.yaml and restarting the app.</p>