Fix typo

docs/DeveloperGuide.md

@@ -156,7 +156,7 @@ The `Model` component,
 The `Storage` component,
 * can save both address book data and user preference data in JSON format, and read them back into corresponding objects.
 * inherits from both `AddressBookStorage` and `UserPrefStorage`, which means it can be treated as either one (if only the functionality of only one is needed).
-* depends on some classes in the `Model` component (because the `Storage` component's job is to save/retrieve objects that belong to the `Model`)
+* depends on some classes in the `Model` component (because the `Storage` component's job is to save/retrieve objects that belong to the `Model`).
 
 ### Common classes