Update mojo sdk to rev f6c8ec07c01deebc13178d516225fd12695c3dc2

mojo/public/tools/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//mojo/public/mojo.gni")
+import("../mojo.gni")
 
 if (use_prebuilt_mojo_shell) {
   copy("copy_mojo_shell") {
     filename = "mojo_shell"
     if (is_win) {
       filename += ".exe"
     }
     sources = [
       "prebuilt/$filename",
     ]
     outputs = [
       "$root_out_dir/$filename",
     ]
   }
 }