added icon.

src/docs/asciidoc/jme3/advanced/mixamo.adoc

@@ -248,7 +248,7 @@ Texture Tab::
 +
 NOTE: If the action is not visible, navigate to the `Dope Sheet Editor` and from the `Action Editor` context, select the `Action`.
 
-.  Click the btn:[Double Down Arrow] button to push the action down into the stack.
+.  Click the icon:angle-double-down[] button to push the action down into the stack.
 .  Beneath the TPose strip you will see a slider. Drag this slider to the right until your strip is nested up against the left margin of the window.
 . Save your file.
 
@@ -276,7 +276,7 @@ Follow the directions for <<jme3/advanced/mixamo#mixamo-animations#,Mixamo Anima
 .  Select the btn:[F] button to save the action.
 .  From the `Info` header, change the layout from `Animation` to the `NLA Editing` layout we created in the <<jme3/advanced/mixamo#creating-the-rigged-animation-file#,Creating The Rigged Animation File>> section of this tutorial. You will see your append `Action` at the top of the list.
 .  From the `NLA Editor` header, select `menu:Add[Add Tracks]`. A new track has now been added to the top of the list.
-.  Click the btn:[Double Down Arrow] button next to the `Action` to push it down into the stack.
+.  Click the icon:angle-double-down[] button next to the `Action` to push it down into the stack.
 .  btn:[LMB] select the strip to make it the only strip selected.
 .  btn:[LMB] drag the selected strip to the right until there is at least a 4 keyframe gap between the furthest strip to the right in the list and the append strip you are dragging.
 +