Fix implicit clone warning in satellite example

[kahgoh]

Fixes the following type of warning:

Notice: temp/satellite.v:54:21: notice: an implicit clone of the slice was done here
   52 |
   53 |     value := preorder[0]
   54 |     preorder = preorder[1..(preorder.len)]
      |                        ~~~~~~~~~~~~~~~~~~~
   55 |
   56 |     left := traverse(value, mut preorder, mut inorder)!
Details: temp/satellite.v:54:21: details: To silence this notice, use either an explicit `a[..].clone()`,
or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.
   52 |
   53 |     value := preorder[0]
   54 |     preorder = preorder[1..(preorder.len)]
      |                        ~~~~~~~~~~~~~~~~~~~
   55 |
   56 |     left := traverse(value, mut preorder, mut inorder)