docs: fix a typo

README.md

@@ -229,7 +229,7 @@ const editor = new JSONEditor({
 
 - `onError(err: Error)`.
   Callback fired when an error occurs. Default implementation is to log an error in the console and show a simple alert message to the user.
-- `onChange(content: Content, previousContent: Content, changeStatus: { contentErrors: ContentErrors, patchResult: JSONPatchResult | null })`. The callback which is invoked on every of the contents, both changes made by a user and programmatic changes made via methods like `.set()`, `.update()`, or `.patch()`.
+- `onChange(content: Content, previousContent: Content, changeStatus: { contentErrors: ContentErrors, patchResult: JSONPatchResult | null })`. The callback which is invoked on every change of the contents, both changes made by a user and programmatic changes made via methods like `.set()`, `.update()`, or `.patch()`.
   The returned `content` is sometimes of type `{ json }`, and sometimes of type `{ text }`. Which of the two is returned depends on the mode of the editor, the change that is applied, and the state of the document (valid, invalid, empty). Please be aware that `{ text }` can contain invalid JSON: whilst typing in `text` mode, a JSON document will be temporarily invalid, like when the user is typing a new string. The parameter `patchResult` is only returned on changes that can be represented as a JSON Patch document, and for example not when freely typing in `text` mode.
 - `onChangeMode(mode: 'tree' | 'text')`. Invoked when the mode is changed.
 - `onClassName(path: Path, value: any): string | undefined`.