Update reference-react-dom.md

Add missing closing bracket

docs/reference-react-dom.md

@@ -38,7 +38,7 @@ ReactDOM.render(
 )
 ```
 
-Render a React element into the DOM in the supplied `container` and return a [reference](/react/docs/more-about-refs.html) to the component (or returns `null` for [stateless components](/react/docs/components-and-props.html#functional-and-class-components).
+Render a React element into the DOM in the supplied `container` and return a [reference](/react/docs/more-about-refs.html) to the component (or returns `null` for [stateless components](/react/docs/components-and-props.html#functional-and-class-components)).
 
 If the React element was previously rendered into `container`, this will perform an update on it and only mutate the DOM as necessary to reflect the latest React element.