[SwiftmailerBridge] Bump allowed versions of swiftmailer

Current version of Swiftmailer is 5.2.1, while (previously to this commit)
the version installed by composer was 5.0.3.

This is rather important, since 5.2.1 closes a security issue that 5.0.3 is
vulnarable to (https://github.com/swiftmailer/swiftmailer/issues/494).
Merge branch '2.3' into 2.4

* 2.3: (35 commits)
  [Form] Fix PHPDoc for builder setData methods The underlying data variable is typed as mixed whereas the methods paramers where typed as array.
  fixed CS
  [Intl] Improved bundle reader implementations
  [Console] guarded against invalid aliases
  switch before_script to before_install and script to install
  fixed typo
  [HttpFoundation] Request - URI - comment improvements
  [Security] Added more tests
  remove `service` parameter type from XSD
  [Intl] Added exception handler to command line scripts
  [Intl] Fixed a few bugs in TextBundleWriter
  [Intl] Updated icu.ini up to ICU 53
  [Intl] Removed non-working $fallback argument from ArrayAccessibleResourceBundle
  Use separated function to resolve command and related arguments
  [SwiftmailerBridge] Bump allowed versions of swiftmailer
  [FrameworkBundle] Remove invalid markup
  [Intl] Added "internal" tag to all classes under Symfony\Component\Intl\ResourceBundle
  Remove routes for removed WebProfiler actions
  [Security] Fix usage of unexistent method in DoctrineAclCache.
  backport more error information from 2.6 to 2.3
  ...

Conflicts:
	.travis.yml
	src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
	src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
	src/Symfony/Component/HttpKernel/Kernel.php
	src/Symfony/Component/Process/PhpExecutableFinder.php