Variable undefined in strict mode in IE 11

[liuhelen10]

I'm encountering this error in IE11: Variable undefined in strict mode

The stack trace points to this line:
https://github.com/webmodules/stickyfill/blob/master/index.js#L61

I'm on version 1.1.1

[liuhelen10]

@coreh I have a PR open for the fix here: #5 do you mind reviewing?