message: placeholder must be string
diff: @@ -9,7 +9,7 @@ import { TextPlugin, PluginRegistry } from '..'
  export interface TextPluginOptions {
  plugins: ((pluginClosure: SlatePluginClosure) => TextPlugin)[]
  registry?: PluginRegistry
  - placeholder?: React.ReactNode
  + placeholder?: string
  }
  export type SlatePluginClosure = React.RefObject<{
  