Hitting tab key on tagsInput results in blinking focus going forward and back

[belfz]

ngTagsInput version: 3.2.0 angular version: 1.5.8 browser: Chrome 60 steps to reproduce:

1. go to project's website,
2. type "test" into demo input,
3. hit tab key on your keyboard,
4. watch carefully: focus "jumps forward" to next element for a short while (in this case, the next anchor element) and then "jumps back" to tags input

I have the solution for this problem - will send a PR shortly.

[belfz]

@mbenford ping!