Add PHP 7.3 test section back

Jenkinsfile

@@ -10,6 +10,18 @@ pipeline {
 				sh 'php composer.phar install --ignore-platform-reqs'
 			}
  		}
+		stage('PHP 7.3') {
+			agent {
+				docker {
+					image 'php:7.3-alpine'
+					args '-u root --privileged'
+				}
+			}
+			steps {
+				sh 'apk add --no-cache git'
+				sh 'php ./vendor/bin/phpunit --colors=never'
+			}
+		}
 		stage('PHP 7.4') {
 			agent {
 				docker {