Update module-reference.md

Typo ("retrieve" becomes "retrieves")

Author: dmarvasti

content/fundamentals/module-reference.md

@@ -22,7 +22,7 @@ export class CatsService {
 
 #### Retrieving instances
 
-The `ModuleRef` instance (hereafter we'll refer to it as the **module reference**) has a `get()` method. This method retrieve a provider, controller, or injectable (e.g., guard, interceptor, etc.) that exists (has been instantiated) in the **current** module using its injection token/class name.
+The `ModuleRef` instance (hereafter we'll refer to it as the **module reference**) has a `get()` method. This method retrieves a provider, controller, or injectable (e.g., guard, interceptor, etc.) that exists (has been instantiated) in the **current** module using its injection token/class name.
 
 ```typescript
 @@filename(cats.service)