Fix doc error for gsutil cp -I
Fix doc error for gsutil cp -I

fishjord/gsutil,ttiurani/gsutil,craigcitro/gsutil,dtjackson/gsutil,mattdr/gsutil,GoogleCloudPlatform/gsutil,GoogleCloudPlatform/gsutil,chriskuehl/gsutil-debian,dimfeld/gsutil,BrandonY/gsutil