reduce UT environments for non-LTS JDKs after EOL

[gzm55]

Now a commit triggers travis testings for eight JDKs, 7-14, and each two endian. I think we don't need to tests for a JDK after half year of EOL, such as JDK 9, 10, 12. That is,

• JDK 7: LTS, target release
• JDK 8: LTS, keep testing
• JDK 9: non-LTS, tested until half year after EOL, now could stop test
• JDK 10: non-LTS, tested until half year after EOL, now could stop test
• JDK 11: LTS, keep testing
• JDK 12: non-LTS, tested until half year after EOL, now could stop test
• JDK 13: non-LTS, tested until half year after EOL
• JDK 14: non-LTS, tested until half year after EOL