[gn] Fix typos in the documentation.

BUG=

Review URL: https://codereview.chromium.org/1579133002

Cr-Original-Commit-Position: refs/heads/master@{#369420}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: b541f71072bc92cfcf37ed9b136c6af2c85cfdf9
1 file changed
tree: 4704ba07113ec1751100821156b1b3e6a0c32453
  1. tools/