Fix some typos in gn's documentation for "copy".

Review URL: https://codereview.chromium.org/1346653004

Cr-Original-Commit-Position: refs/heads/master@{#349218}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c5166a2201bcf4b8738dcbae33709de0831cabc8
2 files changed
tree: 45a359d53141809f6b43b0c466208ff9001028c1
  1. tools/