fix custom selectors in version 2

[janein]

Hi,

would it be possible to make it compatible with jQuery 3.0?

[redmunds]

@janein Thanks for head's up on jQuery 3.0. I don't know of any reason why it wouldn't work, but also not sure of when I'll have time to get to it.

[redmunds]

@janein I have a proposed fix in PR #83 . Please try it out if you have the time.

[janein]

@redmunds thanks. I tried it but it throws an Cannot read property 'className' of undefined on the this[0].className on line 285 on init and on window resize.
But I don't know if it's not a problem with my implementation as it doesn't throw this error everytime (sometime it passes by just fine).

[redmunds]

@janein Thanks for testing -- that's a great catch! Code should make sure that property exists before de-referencing it.

[redmunds]

Fixed in #87

[redmunds]

Re-opening. Leaving this open to remind me to fix custom selectors in version 2.