message: camera: updated e90 camera_definition
  This updates from version 18 to version 20 as contained in
  E90 v1.0.56.
diff: <?xml version="1.0" encoding="UTF-8" ?>
  <mavlinkcamera>
  - <definition version="18">
  + <definition version="20">
  <model>E90</model>
  <vendor>Yuneec</vendor>
  </definition>
  <parameter name="CAM_ZOOM" type="uint32" control="0">
  <description>Camera Zoom</description>
  </parameter>
  + <parameter name="CAM_FILENUMOPT" type="uint8" default="0">
  + <description>File Numbering Option</description>
  + <options>
  + <option name="Auto Reset" value="0" />
  + <option name="Sequential" value="1" />
  + </options>
  + </parameter>
  </parameters>
  <localization>
  <!-- If no appropriate locale is found, the original (above) will be used -->
  