Feature request: moving the scripts-dev section into extra

[Tang Rufus]

Please consider moving the scripts-dev section into extra to avoid $ composer validate complaining it is not defined and the definition does not allow additional properties.

$ composer validate
./composer.json is valid for simple usage with composer but has
strict errors that make it unable to be published as a package:
See https://getcomposer.org/doc/04-schema.md for details on the schema
The property scripts-dev is not defined and the definition does not allow additional properties

Besides, phpstorm also flags the scripts-dev section as an error.

[Vitaliy Krasnoperov]

Done in v0.1.1