Add default value to checkContextObjects doc

Author: JulesBlm

docs/rules/display-name.md

@@ -128,7 +128,7 @@ function HelloComponent() {
 module.exports = HelloComponent();
 ```
 
-### checkContextObjects
+### checkContextObjects (default: `false`)
 
 `displayName` allows you to [name your context](https://reactjs.org/docs/context.html#contextdisplayname) object. This name is used in the React dev tools for the context's `Provider` and `Consumer`.
 When `true` this rule will warn on context objects without a `displayName`.