Symfony 4 support

[andreyserdjuk]

Hi, I suggest to accept this changes partially.
I added support for PHP 7.2, Syfony 4.1, 4.2, updated phpunit version with tests.
Please look on:

• composer.json - don't apply repository name.
• travis.yml - it works for me so you can ignore.
• .gitignore:
  • composer.lock needed to fix working dependecies
  • .phpunit.result.cache - ignore phpunit cache

[andreyserdjuk]

Also you can create tag for merge commit 4.1 or 4.2. Looking forward for your response.