Fix google passive error

[TijmenGraft]

Google 56 introduced passive mode to default be true. The script will
throw errors

[coveralls]

Coverage remained the same at 69.88% when pulling 6fff875 on TijmenGraft:master into 6eb8440 on Mango:master.

[andreasroste]

I support this PR.. get rid of there annoying errors! :)

[joker-777]

@pazguille Would be great if you could merge this.

[nicolaelitvac]

Would be nice to have this merged to master!

[sun]

Not sure whether the copy of the script in index.js also needs to be updated:
https://github.com/Mango/slideout/blob/master/index.js#L209
https://github.com/Mango/slideout/blob/master/index.js#L300

[sun]

The code primarily needs to be fixed in index.js, the files in dist are compiled.

Also note that this issue has been fixed in v2 in the branch new-features already, but that code hasn't been released in any way yet:
https://github.com/Mango/slideout/compare/new-features#diff-168726dbe96b3ce427e7fedce31bb0bcR237

[inoas]

Can this be patched for the current stable release so we can improve lighthouse speeds?

[inoas]

@sun I have taken over what you suggested in #295