Support for GitLab API 4 - Use docker for testing

.mvn/wrapper/maven-wrapper.properties

@@ -0,0 +1 @@
+distributionUrl=https://repo1.maven.org/maven2/org/apache/maven/apache-maven/3.5.0/apache-maven-3.5.0-bin.zip

.travis.yml

@@ -1,10 +1,10 @@
 language: java
-sudo: false
+sudo: required
+services:
+  - docker
 jdk:
 - oraclejdk7
 install:
-- ./gradlew assemble
+- ./mvnw -B -q -Pdocker-gitlab dependency:go-offline verify -DskipTests -Ddocker.skip
 script:
-- ./gradlew check
-before_deploy:
-- ./gradlew deployZip
+- ./mvnw -B -V -Pdocker-gitlab verify

CONTRIBUTING.md

@@ -0,0 +1,9 @@
+# How to contribute
+
+
+* The integration tests need a running Docker infrastructure.
+* To execute these, run `mvn -Pdocker-gitlab clean verify`. This will spawn
+  a new gitlab instance (`pull` needs some time and starting `gitlab-ce` may take up to 3 minutes).
+* To run integration tests in your IDE, you need to execute `mvn -Pdocker-gitlab,docker-ide docker:start`.
+* Once you are done, you may stop gitlab by executing `mvn -Pdocker-gitlab,docker-ide docker:stop`.
+* For more information about the API, take a look at the [documentation](https://gitlab.com/help/api/README.md).

README.md

@@ -1,7 +1,8 @@
 # Gitlab Java API Wrapper
 
 [![Maven Central](https://img.shields.io/maven-central/v/org.gitlab/java-gitlab-api.svg)](http://mvnrepository.com/artifact/org.gitlab/java-gitlab-api)
-
+[![Build Status](https://travis-ci.org/timols/java-gitlab-api.svg?branch=master)](https://travis-ci.org/timols/java-gitlab-api)
 A wrapper for the [Gitlab API](https://gitlab.org) written in Java.
 
 [Documentation](https://timols.github.io/java-gitlab-api) is available in the form of [Javadocs](https://timols.github.io/java-gitlab-api)
+The major version indicates the API version of gitlab.