Fix 'npm run package' in addon-unicode-graphemes #877

Job	Run time
build	1m 2s
test-integration (18, ubuntu, chromium)	3m 42s
test-integration (18, ubuntu, firefox)	3m 36s
test-integration (18, ubuntu, webkit)	3m 35s
lint	58s
test-unit (18, ubuntu)	1m 30s
test-unit (18, macos)	1m 28s
test-unit (18, windows)	7m 55s
test-unit-coverage	1m 2s
release-dry-run (18)	1m 56s
	26m 44s

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