Update .travis.yml

Signed-off-by: slinkydeveloper <francescoguard@gmail.com>

.travis.yml

@@ -3,23 +3,28 @@ branches:
   only:
   - master
   - /^\d+\.\d+$/
+cache:
+  directories:
+    - $HOME/.m2
+before_cache:
+  - rm -rf $HOME/.m2/repository/io/vertx/
 jobs:
   include:
     - stage: test
-      name: "OracleJDK 8"
-      jdk: oraclejdk8
+      name: "OpenJDK 8"
+      jdk: openjdk8
       script: mvn -q clean verify -B
     - if: type != pull_request
       name: "OpenJDK 11"
       jdk: openjdk11
       script: mvn -q clean verify -B
     - if: type != pull_request
-      name: "OracleJDK 8 / native transport"
-      jdk: oraclejdk8
+      name: "OpenJDK 8 / native transport"
+      jdk: openjdk8
       script: mvn -q clean verify -B -PtestNativeTransport
     - if: type != pull_request
-      name: "OracleJDK 8 / domain sockets"
-      jdk: oraclejdk8
+      name: "OpenJDK 8 / domain sockets"
+      jdk: openjdk8
       script: mvn -q clean verify -B -PtestDomainSockets
     - stage: deploy
       name: "Deploy to Sonatype's snapshots repository"