update to centralized travis configuration

Author: jsvd

.travis.yml

@@ -1,15 +1,2 @@
----
-sudo: required
-services: docker
-addons:
-  apt:
-    packages:
-    - docker-ce
-matrix:
-  include:
-  - env: ELASTIC_STACK_VERSION=5.6.15
-  - env: ELASTIC_STACK_VERSION=6.6.1
-  - env: ELASTIC_STACK_VERSION=7.0.0-beta1
-  fast_finish: true
-install: ci/unit/docker-setup.sh
-script: ci/unit/docker-run.sh
+import:
+- logstash-plugins/.ci:travis/travis.yml@1.x

build.gradle

@@ -59,10 +59,3 @@ task cleanGemjar {
 
 clean.dependsOn(cleanGemjar)
 jar.finalizedBy(copyGemjar)
-
-
-// See http://www.gradle.org/docs/current/userguide/gradle_wrapper.html
-task wrapper(type: Wrapper) {
-    description = 'Install Gradle wrapper'
-    gradleVersion = '4.9'
-}

ci/unit/Dockerfile

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.6.4-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.9-bin.zip