Fix links for https://docs.nativescript.org

I've noticed an Angular Expression that isn't working for these links, so I actually replaced to the full URL(https://docs.nativescript.org)

Author: leocaseiro

src/chapters/chapter4.md

@@ -658,4 +658,4 @@ The result of this code is a nice fade-in animation:
 
 Now that you have functional login and list pages, let’s enhance the app’s functionality as a grocery list management tool. In the next chapters you'll add functionality such as email validation, social sharing, and more. And you’ll use one of NativeScript's most useful features to do so: npm modules.
 
-> **TIP**: There are several modules that come out of the box with your NativeScript installation that we did not have time to cover in this guide—including a [location service]({{site.baseurl}}/ApiReference/location/HOW-TO), a [file-system helper]({{site.baseurl}}/ApiReference/file-system/HOW-TO), a [timer module]({{site.baseurl}}/ApiReference/timer/HOW-TO), a [camera module]({{site.baseurl}}/ApiReference/camera/HOW-TO), and a whole lot more. Make sure to peruse the “Modules API” of the docs, or just look around `node_modules/tns-core-modules` to see all of what’s available.
+> **TIP**: There are several modules that come out of the box with your NativeScript installation that we did not have time to cover in this guide—including a [location service](https://docs.nativescript.org/ApiReference/location/HOW-TO), a [file-system helper](https://docs.nativescript.org/ApiReference/file-system/HOW-TO), a [timer module](https://docs.nativescript.org/ApiReference/timer/HOW-TO), a [camera module](https://docs.nativescript.org/ApiReference/camera/HOW-TO), and a whole lot more. Make sure to peruse the “Modules API” of the docs, or just look around `node_modules/tns-core-modules` to see all of what’s available.