Created Jenkinsfile for building app

Jenkinsfile

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+pipeline {
+  agent { dockerfile true } 
+
+  stages {
+
+    stage('Checkout') {
+      steps {
+        checkout scm
+      }
+    }
+
+    stage('Build') {
+      steps {
+        sh 'docker build -t microblog:latest .'
+      }
+    }
+
+  }
+
+}