docs: fix typo (#4944)

It seems that there is an article usage problem here.

content/docs/composition-vs-inheritance.md

@@ -169,4 +169,4 @@ At Facebook, we use React in thousands of components, and we haven't found any u
 
 Props and composition give you all the flexibility you need to customize a component's look and behavior in an explicit and safe way. Remember that components may accept arbitrary props, including primitive values, React elements, or functions.
 
-If you want to reuse non-UI functionality between components, we suggest extracting it into a separate JavaScript module. The components may import it and use that function, object, or a class, without extending it.
+If you want to reuse non-UI functionality between components, we suggest extracting it into a separate JavaScript module. The components may import it and use that function, object, or class, without extending it.