Jenkinsfile: Update deprecated 'stage' syntax

Jenkinsfile

@@ -1,21 +1,25 @@
+#!/usr/bin/env groovy
 properties([[$class: 'BuildDiscarderProperty', strategy: [$class: 'LogRotator', artifactDaysToKeepStr: '30', artifactNumToKeepStr: '10']]])
 
 node('master') {
-    stage 'Pull changes'
-    checkout scm
-
-    stage 'Build data'
-    sh 'mkdir -p build'
-    dir('build') {
-        sh '''
-            cmake -DCMAKE_INSTALL_PREFIX=/install -DCOLOBOT_INSTALL_DATA_DIR=/install/data ..
-            make
-            rm -rf install
-            DESTDIR=. make install
-        '''
+    stage('Pull changes') {
+        checkout scm
     }
 
-    stage 'Archive data'
-    sh 'rm -f data.zip'
-    zip zipFile: 'data.zip', archive: true, dir: 'build/install'
+    stage('Build data') {
+        sh 'mkdir -p build'
+        dir('build') {
+            sh '''
+                cmake -DCMAKE_INSTALL_PREFIX=/install -DCOLOBOT_INSTALL_DATA_DIR=/install/data ..
+                make
+                rm -rf install
+                DESTDIR=. make install
+            '''
+        }
+    }
+
+    stage('Archive data') {
+        sh 'rm -f data.zip'
+        zip zipFile: 'data.zip', archive: true, dir: 'build/install'
+    }
 }