Use jacoco for code coverage

[sjamesr]

Cobertura supports invokespecial at head, but it hasn't had a release in years. JaCoCo on the other hand is still being released relatively frequently.

[coveralls]

Pull Request Test Coverage Report for Build 399

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 82.795%

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Totals
Change from base Build 394:	0.3%
Covered Lines:	948
Relevant Lines:	1145

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💛 - Coveralls