docs: add missing period in shouldComponentUpdate doc (facebook#8720)

docs/docs/reference-react-component.md

@@ -175,7 +175,7 @@ shouldComponentUpdate(nextProps, nextState)
 
 Use `shouldComponentUpdate()` to let React know if a component's output is not affected by the current change in state or props. The default behavior is to re-render on every state change, and in the vast majority of cases you should rely on the default behavior.
 
-`shouldComponentUpdate()` is invoked before rendering when new props or state are being received. Defaults to `true` This method is not called for the initial render or when `forceUpdate()` is used.
+`shouldComponentUpdate()` is invoked before rendering when new props or state are being received. Defaults to `true`. This method is not called for the initial render or when `forceUpdate()` is used.
 
 Returning `false` does not prevent child components from re-rendering when *their* state changes.