When trying to render form with `file` element in it, there is an error:

    Variable "type" does not exist in /home/hsz/projects/MyProject/vendor/braincrafted/bootstrap-bundle/Braincrafted/Bundle/BootstrapBundle/Resources/views/Form/bootstrap.html.twig at line 159

`file_widget` block uses `type` variable, which does not exist. However we can hardcode it to `file` because we are generating `input[type=file]`.
Merge branch 'develop' of github.com:hsz/bootstrap-bundle into hsz-develop

* 'develop' of github.com:hsz/bootstrap-bundle:
  When trying to render form with `file` element in it, there is an error: