title: downgrading bootstrap from 4.3.1 to 3.3.7 with ng-bootstrap
body: <p>I have angular 6 project with bootstrap 4 and ng-bootstrap for modal dialog. Now, since this need to be integertaed to another project which is in angular 3.3.7 so, I was asked to downgrade the bootstrap version. Following are the steps I did:</p>
  
  <pre><code>    npm install bootstrap@3.3.7 --save
  </code></pre>
  
  <p>but after then my ng-bootstrap modal dialog stopped working so, when I try to re-install using below command:</p>
  
  <pre><code>     npm install --save @ng-bootstrap/ng-bootstrap
  </code></pre>
  
  <p>then from ng_modules/bootstrap folder disappears then project shows nothing.
  What am i missing?</p>