fix: define functions as properties
fix: define functions as properties

This is more correct for TS strict mode.
See info here: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/method-signature-style.md

It also is compatible with the unbound-method rule.
react-dropzone/react-dropzone,react-dropzone/react-dropzone,paramaggarwal/react-dropzone,okonet/react-dropzone,react-dropzone/react-dropzone