[ci] Skip JaCoCo on OpenJDK 15 to avoid build failure

Author: harawata

.travis.yml

@@ -1,11 +1,18 @@
 language: java
 
 jdk:
-  - openjdk15
   - openjdk14
   - openjdk11
   - openjdk8
 
+matrix:
+  include:
+    - jdk: openjdk15
+      env: JACOCO_SKIP="-Djacoco.skip=true"
+
+script:
+  - ./mvnw test -B $JACOCO_SKIP
+
 services:
   - docker