travis: moved JDKs to build job

.travis.yml

@@ -1,12 +1,6 @@
 language: java
 sudo: false
 
-jdk:
-  - openjdk8
-  - openjdk9
-  - openjdk11
-  - openjdk13
-
 before_cache:
   - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
   - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
@@ -30,6 +24,11 @@ jobs:
   include:
     # run gradle build
     - stage: build
+      jdk:
+        - openjdk8
+        - openjdk9
+        - openjdk11
+        - openjdk13
       script: ./gradlew build
 
     # publish snapshot to oss.jfrog.org