refactor: extract to method
add icon to option
refactor: move isChecked (option -> util)
refactor: move toInt (background -> util)
ReferenceError: Can't find variable: chrome

file:///home/travis/build/sue445/chrome-gitlab-notifier/src/background.js:128
avoid push to gh-push when pull request
Merge pull request #16 from sue445/issues/14_option_icon

display icon on option page #14

close #14