Add composer requirement for build package

Jenkins/Jenkinsfile-deb-pkg

@@ -20,7 +20,10 @@ pipeline {
         stage('Build') {
             steps {
                 dir ("${BUILD_DIR}") {
-                    sh 'dpkg-buildpackage -us -uc'
+                    sh '''
+                    composer require symfony/flex
+                    dpkg-buildpackage -us -uc
+                    '''
                 }
             }
         }