chore(package): update eslint from 5.0.1 to 5.12.1
chore(package): update eslint from 5.0.1 to 5.12.1

npm run eslint still runs fine, no warnings.

opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay