Fix Editor Scripts manual - no ends_with function

[paweljarosz]

In manuals several times a function "ends_with" is used. There is no built-in "ends_with" function:

 active = function(opts)
        local path = editor.get(opts.selection, "path")
        return ends_with(path, ".lua") or ends_with(path, ".script")
      end,

[vlaaad]

It was an example pseudocode. Perhaps we should replace it with something like path:match("%.lua$")