Add This field is missing RU translation

<source>This field is missing.</source>
Have no translation. Not exists in EN version too. Just forgotten? 
Symfony\Component\Validator\Constraints\Collection()
public $missingFieldsMessage = 'This field is missing.';
merged branch fabpot/moved_validator_4 (PR #7784)

This PR was merged into the 2.1 branch.

Discussion
----------

Add This field is missing RU translation

This PR was submitted on the symfony/Validator read-only repository and moved automatically to the main Symfony repository (closes symfony/Validator#4).

<source>This field is missing.</source>
Have no translation. Not exists in EN version too. Just forgot? 
Symfony\Component\Validator\Constraints\Collection()
public $missingFieldsMessage = 'This field is missing.';

Commits
-------

97c4291 Add This field is missing RU translation
[Validator] fixed wrong URL for XSD
Merge branch '2.1' into 2.2

* 2.1:
  added additional tests to cover invalid argument exceptions in OutputFormatterStyle component
  added a missing check for the provider key
  [Validator] fixed wrong URL for XSD
  [Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions
  [Form] Fixed: String validation groups are never interpreted as callbacks
  if the repository method returns an array ensure that it's internal poin...
  Fix wrong method in findTaggedServiceIds(), add example to docblock.

Conflicts:
	src/Symfony/Bridge/Doctrine/Form/DataTransformer/CollectionToArrayTransformer.php
	src/Symfony/Component/Form/Extension/Core/DataTransformer/DataTransformerChain.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ArrayToPartsTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ChoiceToValueTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ChoicesToValuesTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/DateTimeToArrayTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/DateTimeToRfc3339TransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ValueToDuplicatesTransformerTest.php