liujunchi/osmd-extended: 云教练github库 @ 0.8.5

sschmid 5a7b944efc test: linting (fix no unused variable)		5 lat temu
..
VexFlowConverter_Clef_Test.ts	e3981ad830 refactor: added prefer-const rule and fixed all let variables	7 lat temu
VexFlowMeasure_Test.ts	5a7b944efc test: linting (fix no unused variable)	5 lat temu
VexFlowMusicSheetDrawer_Test.ts	4fa617e2a8 test: unskip 4 skipped tests, comment out 5th skipped, faulty test	5 lat temu