我正在关注聚合物（2.0）官方教程以运行和测试示例应用程序。使用聚合物测试或聚合物测试-l chrome 运行测试时，会显示以下错误：
Tests failed: {"value":{"stacktrace":"org.openqa.selenium.WebDriverException: Timed out waiting for driver server to start.\nBuild info: version: \u00273.7.1\u0027, revision: \u00278a0099a\u0027, time: \u00272017-11-06T21:07:36.161Z\u0027\nSystem info: host: \u0027silverdust\u0027, ip: \u0027127.0.1.1\u0027, os.name: \u0027Linux\u0027, os.arch: \u0027amd64\u0027, os.version: \u00274.13.0-39-generic\u0027, java.version: \u00271.8.0_162\u0027\nDriver info: driver.version: unknown\n\tat org.openqa.selenium.remote.service.DriverService.waitUntilAvailable(DriverService.java:192)\n\tat org.openqa.selenium.remote.service.DriverService.start(DriverService.java:178)\n\tat org.openqa.selenium.remote.server.ServicedSession$Factory.apply(ServicedSession.java:207)\n\tat org.openqa.selenium.remote.server.ActiveSessionFactory.lambda$apply$11(ActiveSessionFactory.java:167)\n\tat java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)\n\tat java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)\n\tat java.util.stream.ReferencePipeline$11$1.accept(ReferencePipeline.java:373)\n\tat java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)\n\tat java.util.Spliterators$ArraySpliterator.tryAdvance(Spliterators.java:958)\n\tat java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:126)\n\tat java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:498)\n\tat java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485)\n\tat java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)\n\tat java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152)\n\tat java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)\n\tat java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:464)\n\tat org.openqa.selenium.remote.server.ActiveSessionFactory.apply(ActiveSessionFactory.java:170)\n\tat org.openqa.selenium.remote.server.NewSessionPipeline.lambda$null$1(NewSessionPipeline.java:44)\n\tat java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
我正在使用最新版本的ubuntu 以及 nodejs（9.x）。我正在使用 polymer-cli 来自动 - 生成文件。我该如何解决这个问题？