title: Jenkins branch specifier can't be set to subfolder
body: <p>I have a project repository in Bitbucket in which I have <code>master</code> branch and <code>dev</code> branch. </p>
  
  <p>I want to build and deploy to FTP server. <code>Dev</code> branch consists of two folders, where one is <code>backend</code> - laravel, the other is <code>frontend</code> - angular. </p>
  
  <p>Now in Jenkins, I have set <code>Branch specifier</code> to: <code>*/dev/frontend/.*</code></p>
  
  <p>But this path does not work because when I start build, it fails:</p>
  
  <pre><code>... 
  + npm install
  npm WARN saveError ENOENT: no such file or directory, open '/var/jenkins_home/workspace/Project/package.json'
  npm WARN enoent ENOENT: no such file or directory, open '/var/jenkins_home/workspace/Project/package.json'
  npm WARN Project No description
  npm WARN Project No repository field.
  npm WARN Project No README data
  npm WARN Project No license field.
  ... and the rest ...
  </code></pre>
  
  <p>My build shell commands are:</p>
  
  <pre><code>npm install
  npm run ng -- build --prod
  </code></pre>
  
  <p>Is there some plugin or some other way to get into the frontend folder so it can read the files required for build?</p>