fix: highlight country from preferred list

[denkorolenko]

When we define a preferredCountries property, we have a list of the preferred countries on the top of the drop-down menu. But when we open a drop-down, the selected country by default will be in general list, not in a preferredCountries list. See a demo:

In this case, preferredCountries is hidden from the user. He will not expect to find it and will not look for it.

Instead, let's try to select a country from the preferredCountries list. See a demo:

[coveralls]

Coverage increased (+0.01%) to 94.186% when pulling 5bdbb79 on mycsHQ:fix-highlight-country into e9de24d on patw0929:master.

[denkorolenko]

I would like to add a unit test, but I have an error after ./node_modules/.bin/jest command:
Cannot find module 'react' from 'RootModal.test.js'

yarn test command doesn't work for me, it can't find test file
No tests found related to files changed since last commit.

@patw0929, Do you know what can be a problem?

[patw0929]

Awesome! Thank you 👍

The missing module error of react when running test, please install peer dependency packages by following command:

yarn add react@^15.4.2 react-dom@^15.4.2 prop-types@~15.5.8 --peer

[denkorolenko]

@patw0929 it works, thanks. I will add a test.

[denkorolenko]

I added a small test, @patw0929 could you pls take a look? ;)

[patw0929]

LGTM 💯
Thank you for your contribution! Will merge later.