Add support of symfony 3.4/4.0

[gregurco]

Add symfony lts version and 3.4 to travis Remove varci.yml

• [ ] Bug fix
• [x] New feature
• [ ] BC breaks
• [ ] Deprecations
• [x] Tests pass

Fixed tickets: [#150] License: MIT

[gregurco]

@florianpreusner I added symfony 3.4 but I forgot about 4.0... :slightly_frowning_face:

[gregurco]

@florianpreusner I think it's ready for merging but something is wrong with SensioLabsInsight :slightly_frowning_face:

[florianpreusner]

SensioLabsInsight seems to work again.