add nebula snapshots to update sites

Author: jantje

io.sloeber.product/arduino.product

@@ -368,6 +368,7 @@ rights to a jury trial in any resulting litigation.</p>
       <repository location="http://download.eclipse.org/releases/neon" enabled="true" />
       <repository location="http://eclipse.baeyens.it/update/V4/nightly" enabled="false" />
       <repository location="http://eclipse.baeyens.it/update/V4/stable" enabled="true" />
+      <repository location="http://download.eclipse.org/nebula/snapshot" enabled="true" />
    </repositories>
 
    <preferencesInfo>