firmware: use monospace font to display contents

The upgrade progress picks up the actual output of the command line
firmware tools, which expects monospaced output in order to be fully
readable and aligned.  Looks a bit archaic, but not worse than before.

src/opnsense/mvc/app/views/OPNsense/Core/firmware.volt

@@ -214,7 +214,7 @@ POSSIBILITY OF SUCH DAMAGE.
                     </table>
                 </div>
                 <div id="progress" class="tab-pane fade in">
-                    <textarea name="output"  id="update_status" class="form-control" rows="10" wrap="hard" readonly style="max-width:100%;"></textarea>
+                    <textarea name="output" id="update_status" class="form-control" rows="10" wrap="hard" readonly style="max-width:100%; font-family: monospace;"></textarea>
                 </div>
             </div>
         </div>