8218692: Switch to JCov build which supports byte code version 57
Reviewed-by: erikj
/build/
/dist/
/.idea/
nbproject/private/
/webrev
/.src-rev
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.DS_Store
.metadata/
.recommenders/
test/nashorn/script/external
test/nashorn/lib
NashornProfile.txt
**/JTreport/**
**/JTwork/**