Run maven in batch-mode (#112)

Author: mathbagu

Diff for: .travis.yml

@@ -15,7 +15,7 @@ addons:
 install:
 # Build powsybl-core
 - git clone https://github.com/powsybl/powsybl-core powsybl/powsybl-core
-- pushd powsybl/powsybl-core && mvn -DskipTests install && popd
+- pushd powsybl/powsybl-core && mvn --batch-mode -DskipTests install && popd
 
 script:
-- mvn clean verify sonar:sonar
+- mvn --batch-mode clean verify sonar:sonar