Set knp_menu.enable as a boolean instead of scalar

[tbordinat]

Setting something else than a boolean ends in an exception about the next element, "main_menu"

An exception has been thrown during the rendering of a template ("The menu "adminlte_main" is not defined.").

With the enable attribute as a boolean, the exception is now understandable.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I updated the documentation (see here)
• I agree that this code is used in AdminLTEBundle and will be published under the MIT license

[kevinpapst]

Thanks @Ultiiiiii for another PR!
I will give this a try soon and come back to you in the next days.

[tbordinat]

I had to abort my Skype demo because I typed enable instead of true .. :-(
Haha

[kevinpapst]

Thank you @Ultiiiiii 👍