docs: fix sandbox URL (#1303)

The sandbox has moved to a new URL some time ago; replace occurrences
with the new URL.

Signed-off-by: Diego Rondini <diego.rondini@kynetics.com>

docs/content/gettingstarted.md

@@ -7,7 +7,7 @@ weight: 20
 
 We offer a sandbox installation that is free for everyone to try out hawkBit's [Management UI](/hawkbit/ui/),
 [Management API](/hawkbit/apis/management_api/), and [Direct Device Integration API](/hawkbit/apis/ddi_api/):  
-**[<i class="fas fa-desktop">&nbsp;</i> https://hawkbit.eclipse.org](https://hawkbit.eclipse.org)**
+**[<i class="fas fa-desktop">&nbsp;</i> https://hawkbit.eclipseprojects.io](https://hawkbit.eclipseprojects.io)**
 
 {{% warning %}}
 The sandbox is a shared installation that will be reset from time to time. Therefore, it is not allowed to upload