Update django-countries to 2.1.2, override country name for Taiwan

[ECOM-475](https://openedx.atlassian.net/browse/ECOM-475)

* Update django-countries to 2.1.2 to get setting that allows us to override country names.
* Override the country name for Taiwan

Reviewers: @dianakhuang @stephensanchez 
FYI: @jbau @chrisndodge