Fix grammar-o in gn's help.

Change-Id: Id6d327ce5631c6078a45760eee7597a3dfc90416
Reviewed-on: https://chromium-review.googlesource.com/1000023
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#548882}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 743a7a884c8d1008067f662c003c7e1d31c39d73

tools/gn/runtime_deps.cc

diff --git a/tools/gn/runtime_deps.cc b/tools/gn/runtime_deps.cc
index 0545617..f0a242d 100644
--- a/tools/gn/runtime_deps.cc
+++ b/tools/gn/runtime_deps.cc
@@ -253,7 +253,7 @@
   many actions into one logic unit, and the "data"-ness of A's dependency is
   lost. Solutions:
 
-   - List the outputs of the action in it's data section (if the results of
+   - List the outputs of the action in its data section (if the results of
      that action are always runtime files).
    - Have B list the action in data_deps (if the outputs of the actions are
      always runtime files).