v15.0.0

• BREAKING Require Node.js 12
• BREAKING (in case you relied on indentation) JSON reporter: beautify output using 2-space indentation
• Fix #152: results were being overwritten when a large number of files was used
• use an Array for the Java command (#166)
• Switch to execFile (#168)
• Switch to async.mapLimit (#170); this should speed things up with a large number of files and a number of threads > 2
• Improve CI; add Windows x86 run
• Various small refactoring patches

v14.5.0...v15.0.0