zoiets zou moeten werken

pipeline {
  agent any
  stages {
    if(env.BRANCH_NAME == 'master') {
      stage('Checkout') {
        steps {
          dir(path: '/var/www/html/test') {
            git(url: 'https://github.com/stevenliebregt/test-cd.git', branch: 'master', credentialsId: 'github')
          }
        }
      }
      stage('Composer install') {
        steps {
          sh 'composer install'
        }
      }
    }
  }
}