Switch to JDK 11 for CI builds

.drone.yml

@@ -11,7 +11,7 @@ steps:
     depth: 10
     skip_verify: true
 - name: test-online
-  image: maven:3.5-jdk-8-alpine
+  image: maven:3-jdk-11-slim
   commands:
   - export VAULT_VERSION=1.0.1
   - wget https://releases.hashicorp.com/vault/${VAULT_VERSION}/vault_${VAULT_VERSION}_linux_amd64.zip
@@ -24,7 +24,7 @@ steps:
     branch:
     - master
 - name: test-offline
-  image: maven:3.5-jdk-8-alpine
+  image: maven:3-jdk-11-slim
   commands:
   - mvn clean test -Dtest='!HTTPVaultConnectorTest'
   when:

.travis.yml

@@ -3,7 +3,7 @@ branches:
     - master
 language: java
 jdk:
-  - oraclejdk8
+  - openjdk11
 dist: trusty
 install: true
 addons: