fix: add debounce to computeUrl to remove angular2 multiple api error

[MrChoclate]

fix #67

It fixes the issue on my angular2 project.

@ebidel is this what you meant?:

the loading code can probably use a debouncer

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[MrChoclate]

I signed it!

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CLAs look good, thanks!

[ebidel]

Thanks for the PR. I have some reservations about the approach. Namely, it will make all maps components 300ms slower. How short can you make the time before it no longer works?

[MrChoclate]

It seems that wait=0 remove the error. It is way far beyond my expertise to understand why. So someone should check that it is correct.

Did I correctly understand your review?

[MrChoclate]

My hypothesis is that Angular code is executed synchronously and is not letting the callback executed so that all the attributes of the Polymer element are properly set before the callback is executed.

Anyway, this PR won't slow anymore all maps components. But it will be great to have a comment explaining why it is necessary.