adding npm install

jenkins/Jenkinsfile

@@ -31,7 +31,17 @@ pipeline {
             }
             steps {
                 sh "echo 'done building'"
-                sh "sleep 15"
+            }
+        }
+        stage('npm install') {
+            agent {
+                docker {
+                    image 'node:6-alpine'
+                    args '-p 3000:3000'
+                }
+            }
+            steps {
+                sh 'npm install'
             }
         }
     }