Fix compile errors. Use Xtend 2.6.2.
Use Java 8 due to Xtend requirement.
Fix Travis setting to use Java 8.
Fix travis setting to notify build errors.
Merge branch 'master' into 59_refactor_sonar

Conflicts:
	src/main/java/net/exkazuu/probe/github/GithubRepositoryInfo.xtend
	src/main/java/net/exkazuu/probe/sonar/SonarInfo.xtend