Update maven and jdk variables for Jenkins

stack/Jenkinsfile

diff --git a/stack/Jenkinsfile b/stack/Jenkinsfile
index aebb217..16f23f8 100644
--- a/stack/Jenkinsfile
+++ b/stack/Jenkinsfile
@@ -25,8 +25,8 @@
     }
 
     tools {
-        maven 'Maven 3 (latest)'
-        jdk 'JDK 1.8 (latest)'
+        maven 'maven_3_latest'
+        jdk 'jdk_1.8_latest'
     }
 
     options {