fix error

Author: greg-rychlewski

lib/ecto/adapters/myxql.ex

@@ -550,7 +550,7 @@ defmodule Ecto.Adapters.MyXQL do
     end
 
     {args, cmd_opts} = args_cmd_opts(opts, opt_args, cmd_opts)
-    cmd = String.to_charlist(command)
+    cmd = String.to_charlist(cmd)
 
     cmd =
       if Path.type(cmd) == :absolute do