Update options-lifecycle-hooks.md (vuejs#1262)

Author: fishmandev

src/api/options-lifecycle-hooks.md

@@ -140,7 +140,7 @@ All lifecycle hooks automatically have their `this` context bound to the instanc
 
 - **Details:**
 
-  Called after a component instance has been unmounted. When this hook is called, all directives of the component instance have been unbound, all event listeners have been removed, and all child component instance have also been unmounted.
+  Called after a component instance has been unmounted. When this hook is called, all directives of the component instance have been unbound, all event listeners have been removed, and all child component instances have also been unmounted.
 
   **This hook is not called during server-side rendering.**