Relax dependencies on Kdyby and allow install newer versions

[fprochazka]

I haven't found any direct dependency on Kdyby, so I suppose it can be relaxed

$ composer update
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for zenify/doctrine-migrations ~2.1 -> satisfiable by zenify/doctrine-migrations[v2.1.0].
    - Can only install one of: kdyby/doctrine[2.0.x-dev, 3.0.x-dev].
    - Can only install one of: kdyby/doctrine[2.0.x-dev, 3.0.x-dev].
    - zenify/doctrine-migrations v2.1.0 requires kdyby/doctrine ~2.0 -> satisfiable by kdyby/doctrine[2.3.x-dev, 2.0.x-dev].
    - Conclusion: don't install kdyby/doctrine 2.3.x-dev
    - Installation request for kdyby/doctrine ~3.0@dev -> satisfiable by kdyby/doctrine[3.0.x-dev].

[TomasVotruba]

I'm against optional dependencies. This can be dropped.