Docserver: Have the what's new page for apps not say "What's New in Extensions"

NOTRY=True

Review URL: https://codereview.chromium.org/441753003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287470 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/docs/templates/public/apps/whats_new.html

-{{+partials.standard_extensions_article
+{{+partials.standard_apps_article
     article:(articles.whats_new
-             changes:whatsNew.apps) /}}
+             changes:whatsNew.apps) /}}
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