Merged in sorinvasile/gazebo_tutorials/sorinvasile/replaced-the-3d-warehouse-link-which-is--1493894809018 (pull request #428)

Replaced the 3D Warehouse link which is not longer valid to the new location

Approved-by: Louise Poubel <[email protected]>
Approved-by: Ian Chen <[email protected]>

Author: iche033

build_model/tutorial.md

@@ -26,7 +26,7 @@ SDF Models can range from simple shapes to complex robots. It refers to the `<mo
 
 This step involves gathering all the necessary 3D mesh files that are required to build your model. Gazebo provides a set of simple shapes: box, sphere, and cylinder. If your model needs something more complex, then continue reading.
 
-Meshes come from a number of places. [Google's 3D warehouse](http://sketchup.google.com/3dwarehouse/) is a good repository of 3D models. Alternatively, you may already have the necessary files. Finally, you can make your own meshes using a 3D modeler such as [Blender](http://blender.org) or [Sketchup](http://sketchup.google.com).
+Meshes come from a number of places. [Google's 3D warehouse](https://3dwarehouse.sketchup.com/index.html) is a good repository of 3D models. Alternatively, you may already have the necessary files. Finally, you can make your own meshes using a 3D modeler such as [Blender](http://blender.org) or [Sketchup](http://sketchup.google.com).
 
 Gazebo requires that mesh files be formatted as STL or Collada, with Collada being the preferred format.