Update AUTHORS file with @vivaldi.com domain

Change-Id: I98f2cab3f8597e2bdb48d40999e13a7008a34096
Reviewed-on: https://chromium-review.googlesource.com/923738
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539542}

AUTHORS

@@ -956,4 +956,5 @@ Torchmobile Inc.
 Upwork <*@cloud.upwork.com>
 Venture 3 Systems LLC <*@venture3systems.com>
 Vewd Software AS <*@vewd.com>
+Vivaldi Technologies AS <*@vivaldi.com>
 Yandex LLC <*@yandex-team.ru>