fixed image name

Author: farah-alyasari

articles/azure-maps/media/tutorial-iot-hub-maps/connectionstring.png renamed to articles/azure-maps/media/tutorial-iot-hub-maps/connection-string.png

@@ -154,7 +154,7 @@ In order to connect to the IoT Hub, a device must be registered. To register a d
 
 3. Save the **Primary Connection String** of your device to use it in a later step, in which you need to change a placeholder with this connection string.
 
-    ![add-device](./media/tutorial-iot-hub-maps/connectionString.png)
+    ![add-device](./media/tutorial-iot-hub-maps/connection-string.png)
 
 ## Upload geofence