fix ImageSource link use full url (#29)

Author: jcassidyav

plugins/social-share.md

@@ -25,7 +25,7 @@ import * as SocialShare from "@nativescript/social-share";
 
 ### shareImage(ImageSource image, [optional] String subject)
 
-The `shareImage()` method expects an [`ImageSource`](/api-reference/classes/imagesource.html) object. The code below loads an image from the app and invokes the share widget with it:
+The `shareImage()` method expects an [`ImageSource`](https://docs.nativescript.org/api-reference/classes/imagesource.html) object. The code below loads an image from the app and invokes the share widget with it:
 
 ```JavaScript
 // ------------ JavaScript ------------------