Update reference-react-component.md (#9863)

Grammatical edit to match same statement in state-and-lifecycle.html

docs/reference-react-component.md

@@ -359,7 +359,7 @@ In particular, `this.props.children` is a special prop, typically defined by the
 
 The state contains data specific to this component that may change over time. The state is user-defined, and it should be a plain JavaScript object.
 
-If you don't use it in `render()`, it shouldn't be on the state. For example, you can put timer IDs directly on the instance.
+If you don't use it in `render()`, it shouldn't be in the state. For example, you can put timer IDs directly on the instance.
 
 See [State and Lifecycle](/react/docs/state-and-lifecycle.html) for more information about the state.