[docs] Update style guide's mention of blink's path

TBR=pkasting@chromium.org

Change-Id: I906a7918779e5dc17d4cc35406470bca43e1deb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062912Reviewed-by: Tom McKee <tommckee@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Tom McKee <tommckee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742250}

styleguide/c++/c++.md

@@ -16,7 +16,7 @@ You can propose changes to this style guide by sending an email to
 request review for a change to this file. If there's no consensus,
 `src/styleguide/c++/OWNERS` get to decide.
 
-Blink code in `third_party/WebKit` uses [Blink style](blink-c++.md).
+Blink code in `third_party/blink` uses [Blink style](blink-c++.md).
 
 ## Modern C++ features