Merge two translation files with setTranslation

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[ ] feature request

Current behavior having this two translate files: translation1:

{
  "HOME": {
    "TITLE": "Hello Angular with ngx-translate!",
    "SELECT": "Change language"
  }
}

translation2:

{
   "HOME": {
      "TITLE": "Hello Angular with ngx-translate! version2"
    }
 }`

And doing: translate.setTranslation('en', translation2, true);

I get:

{
  "HOME": {
    "TITLE": "Hello Angular with ngx-translate!",
    "SELECT": "Change language"
  }
}

Expected/desired behavior

{
  "HOME": {
    "TITLE": "Hello Angular with ngx-translate! version2",
    "SELECT": "Change language"
  }
}

Reproduction of the problem

http://plnkr.co/edit/ur5zrnrteKPbbmGdUAEy

What is the expected behavior?

What is the motivation / use case for changing the behavior?

Merge two translation files

Please tell us about your environment:

ngx-translate version: 8.0.0
Angular version: 4.4.3
Browser: Chrome 61.0.3163.79

ngx-translate / core

Merge two translation files with setTranslation #687