message: update node and yarn versions to match generator-jhipster
diff: <!-- Build properties -->
  <java.version>1.8</java.version>
  <maven.version>3.0.0</maven.version>
  - <node.version>v6.11.5</node.version>
  - <yarn.version>v1.2.1</yarn.version>
  + <node.version>v8.9.4</node.version>
  + <yarn.version>v1.3.2</yarn.version>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
  <project.testresult.directory>${project.build.directory}/test-results</project.testresult.directory>
  