Compile against Java 8

[ahmedre]

This fixes #28.

[codecov]

Codecov Report

Merging #30 (b4b73be) into master (54f36a1) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #30   +/-   ##
=========================================
  Coverage     93.80%   93.80%           
  Complexity      136      136           
=========================================
  Files            20       20           
  Lines           500      500           
  Branches         45       45           
=========================================
  Hits            469      469           
  Misses           20       20           
  Partials         11       11           

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