FIX gumby.inview.js to allow empty data-target attribute

If data-target attribute is set but has no value, targetStr will be true and a js error will occur. Fix: check for length of the attribute value (it will be boolean true if there's no value, length of boolean == undefined (so false)).
Merge pull request #2 from micschk/patch-1

FIX gumby.inview.js to allow empty data-target attribute