Fix Zephyr image (#334)

* Fix Zephyr image

* Update

Author: pablogs9

_docs/tutorials/core/first_application_rtos/index.md

@@ -11,7 +11,7 @@ Micro-ROS currently supports three different RTOS, namely NuttX, FreeRTOS, and Z
  <tr>
   <td style="width:33%; text-align:center; vertical-align:bottom; font-weight:bold;"><a href="nuttx/"><img style="margin-left:auto; margin-right:auto; padding-bottom:5px;" width="125" height="125" src="https://upload.wikimedia.org/wikipedia/commons/b/b0/NuttX_logo.png"><br/>NuttX</a></td>
   <td style="width:33%; text-align:center; vertical-align:bottom; font-weight:bold;"><a href="freertos/"><img style="margin-left:auto; margin-right:auto; padding-bottom:5px;" width="263" height="100" src="https://upload.wikimedia.org/wikipedia/commons/4/4e/Logo_freeRTOS.png"><br/>FreeRTOS</a></td>
-  <td style="width:33%; text-align:center; vertical-align:bottom; font-weight:bold;"><a href="zephyr/"><img style="margin-left:auto; margin-right:auto; padding-bottom:5px;" width="220" height="114" src="https://upload.wikimedia.org/wikipedia/commons/2/2d/Zephyr-logo.png"><br/>Zephyr</a></td>
+  <td style="width:33%; text-align:center; vertical-align:bottom; font-weight:bold;"><a href="zephyr/"><img style="margin-left:auto; margin-right:auto; padding-bottom:5px;" width="220" height="114" src="https://www.linuxfoundation.org/wp-content/uploads/zephyr-color.svg"><br/>Zephyr</a></td>
  </tr>
 </table>