add jenkins tests

Jenkinsfile

@@ -0,0 +1,25 @@
+pipeline {
+    agent any
+
+    stages {
+        stage('PHP 7.1') {
+            steps {
+                sh '/usr/local/bin/composer-php7.1 install'
+                sh 'php7.1 /usr/local/bin/phpunit-7'
+            }
+        }
+        stage('PHP 7.3') {
+            steps {
+                sh '/usr/local/bin/composer-php7.3 update'
+                sh 'php7.3 /usr/local/bin/phpunit-9'
+            }
+        }
+        stage('PHP 7.4') {
+            steps {
+                sh '/usr/local/bin/composer-php7.4 update'
+                sh 'php7.4 /usr/local/bin/phpunit-9'
+            }
+        }
+    }
+}
+