Fix environment variable

Author: iluwatar

.travis.yml

@@ -18,7 +18,7 @@ install:
 
 after_success:
 - mvn clean test jacoco:report coveralls:report
-- mvn clean org.jacoco:jacoco-maven-plugin:prepare-agent package sonar:sonar -Dsonar.host.url=https://sonarqube.com -Dsonar.login=SONAR_TOKEN
+- mvn clean org.jacoco:jacoco-maven-plugin:prepare-agent package sonar:sonar -Dsonar.host.url=https://sonarqube.com -Dsonar.login=$SONAR_TOKEN
 - bash update-ghpages.sh
 
 # use latest java version available instead of travis default