Added alex.gaynor@gmail.com to AUTHORS

Previous commits have been at my Mozilla address, but I've also been involved in Chromium in my personal capacity.

Change-Id: I1ef97b84bbf947b7e5e957249c8cc01e8410a41d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2394675Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804924}

AUTHORS

@@ -43,6 +43,7 @@ Aldo Culquicondor <alculquicondor@gmail.com>
 Aleksandar Stojiljkovic <aleksandar.stojiljkovic@intel.com>
 Alex Gabriel <minilogo@gmail.com>
 Alex Gartrell <agartrell@cmu.edu>
+Alex Gaynor <alex.gaynor@gmail.com>
 Alex Henrie <alexhenrie24@gmail.com>
 Alex Scheele <alexscheele@gmail.com>
 Alexander Douglas <agdoug@amazon.com>