Update webRequest.html document to fix a syntax error

This patch just fixes a syntax error in the document for developers.

Change-Id: Id128a69bde993c93d8550c6d0d45e14c7ebc0481
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1776150
Auto-Submit: Takashi Toyoshima <toyoshim@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692137}

chrome/common/extensions/docs/templates/intros/webRequest.html

@@ -121,7 +121,7 @@ complete nor stable.
 <p>
 <span class="availability">Starting from Chrome 76</span>, header modifications
 affect Cross-Origin Resource Sharing (CORS) checks. If modified headers for
-cross-origin requests do not meet a criteria, it will results in sending a CORS
+cross-origin requests do not meet the criteria, it will result in sending a CORS
 preflight to ask the server if such headers can be accepted.
 If you really need to modify headers in a way to violate the CORS protocol, you
 need to specify <code>'extraHeaders'</code> in <code>opt_extraInfoSpec</code>.