Modify component to use PopperJS

[LouizFC]

Greetings.

I propose to use PopperJS. I know that adding a dependency to a project has a cost, but I think that PopperJS can be very beneficial to this project. It allows for further customization and covers most corner cases on positioning without needing to implement custom logic.

It has been adopted by the some major frameworks like bootstrap, foundation and element-ui.

I will get familiar with the source code and see If I can submit a PR.

Thank you.

[fritx]

@LouizFC would be appreciated if that could out-sourcing some logic from vue-at.
Also, looks good that might solve #5

[LouizFC]

closing this as wontfix, This issue is stale for 5 years, and I no longer use vue as my primary frontend framework

[fritx]

@LouizFC I'm very sorry for that