Trivial: Removing gendered pronouns from watchlists.py.

BUG=879943

Change-Id: Ic0c4351571ec0be9742610a86d079cffc09cdfa0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1861474
Auto-Submit: Chris Hall <chrishall@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@google.com>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>

watchlists.py

@@ -6,8 +6,8 @@
 """Watchlists
 
 Watchlists is a mechanism that allow a developer (a "watcher") to watch over
-portions of code that he is interested in. A "watcher" will be cc-ed to
-changes that modify that portion of code, thereby giving him an opportunity
+portions of code that they are interested in. A "watcher" will be cc-ed to
+changes that modify that portion of code, thereby giving them an opportunity
 to make comments on codereview.chromium.org even before the change is
 committed.
 Refer: http://dev.chromium.org/developers/contributing-code/watchlists