It's confirmed as Selenium bug. Endpoints for contexts were accidentally deleted. Working on a PR to Selenium

https://github.com/appium/java-client/issues/36

回滚到 2.41.0 吧

<dependency>
  <groupId>org.seleniumhq.selenium</groupId>
  <artifactId>selenium-java</artifactId>
  <version>2.41.0</version>
  <scope>test</scope>
</dependency>