chore(travis): Use trusty for oraclejdk8 support

[tisoft]

Oracle JDK 8 is preinstalled in trusty, but isn't in xenial anymore. So for the time beeing fix the distribution to trusty.

[coveralls]

Pull Request Test Coverage Report for Build 113

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.083%

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Totals
Change from base Build 104:	0.0%
Covered Lines:	540
Relevant Lines:	545

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💛 - Coveralls