Support uppercase hash override in amp-geo.

[gmajoulet]

Support uppercase hash override in amp-geo to make sure both options work:

• https://foo.bar#amp-geo=de
• https://foo.bar#amp-geo=DE

[jpettitt]

I don't really like this. The problem I have with it is the countries specified in the json config must be lower case. Allowing upper case here when we don't allow it in the data we're matching is likely to cause confusion. The doc is clear that it's the lowercase ISO 3166-1 alpha-2 country code.

Why is it needed?

[gmajoulet]

It is not needed, I spent a few minutes thinking my implementation of the component was wrong, when I actually was using an uppercase country code. Thought I could help someone.
Being consistent makes a lot more sense, thanks for the review.

[jpettitt]

It might make sense if you also added

ISOCountryGroups[group] = ISOCountryGroups[group].map(country => country.toLowerCase());

in matchCountryGroups_ that would force the config to lower case too which would make it more robust against users using an uppercase config by mistake.

[jpettitt]

LGTM