Fix getTranslation method for plurals with context

[lukasgeiter]

In case of plural translations that have multiple contexts (one of them being the default context) getTranslation() returns the wrong result. Instead of the correct string it returns the whole array of plural translations. The cause of this is the this part of the method:

if (!(translated instanceof Array) && translated.hasOwnProperty('')) {
      // As things currently stand, the void key means a void context for easygettext.
      translated = [translated['']]
}

This code assumes that the value of translated[''] is a singular message (i.e. a string) and therefore wraps it in an array. This PR fixes this by removing the array and moving the existing normalization logic after this code.

[kemar]

Thank you @lukasgeiter Kudos for the clean explanation and the tests.

I published a new release with your fix: https://github.com/Polyconseil/vue-gettext/releases/tag/v2.1.3