fix: only use checkVisibility if supported

[ryangjchandler]

Closes #24.

This is the simplest fix to the problem, simply checking to see if the method is supported in the browser.

[ryangjchandler]

FYI @nunomaduro – tsc wasn't playing nice so I can't actually build the dist files, it's complaining about Array.includes() which is unrelated to my change.