Changed aria-live attribute value from polite to assertive

[RaphStein]

For ngMessages directive ngAria generates aria-live with value assertive and not polite.

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[Narretz]

Hi, thanks for the PR! Can you please sign the CLA?

[RaphStein]

Hi, i have signed the CLA.

[googlebot]

CLAs look good, thanks!

[marcysutton]

"Assertive" was added for a reason: so that feedback would be given immediately as users type in text inputs. We talked about making this a configuration option, was that not considered?

[Narretz]

I'm not sure if I follow; is this now incorrect? It was only a change in the docs to match the behavior in code, so I assumed it was safe.

[marcysutton]

Ah ha, I totally read that wrong! Disregard. :)