Add OpenJDK8 and remove OracleJDK7 so we can use trusty.

[ruebot]

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[codecov]

Codecov Report

Merging #39 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #39   +/-   ##
=======================================
  Coverage   43.41%   43.41%           
=======================================
  Files          42       42           
  Lines         850      850           
  Branches      148      148           
=======================================
  Hits          369      369           
  Misses        437      437           
  Partials       44       44

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[ruebot]

@ianmilligan1 we'll want to merge this before #38.