composer-warning: please add ext-key to composer.json

[Thomas Wittich]

Dear Planers,

just a tiny hint, a warning from composer when using your extension:

TYPO3 Extension Package "plan2net/webp", does not define extension key in composer.json.
Specifying the extension key will be mandatory in future versions of TYPO3 (see: https://docs.typo3.org/m/typo3/reference-coreapi/master/en-us/ExtensionArchitecture/ComposerJson/Index.html#extra)

Thank you, Thomas

[Wolfgang Klinger]

see #48 fixed in March, tagged a new version now