[Extensions Docs] Use allowlist in shared modules documentation

https://crrev.com/9486b056 updated shared module code to use allowlist;
update the documentation to match.

TBR=mkearney@chromium.org

Bug: 842354
Change-Id: I2663de6faa05a7322ee9c63bfab73c6777da1532
Reviewed-on: https://chromium-review.googlesource.com/1068206Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560758}

chrome/common/extensions/docs/templates/articles/shared_modules.html

@@ -38,9 +38,9 @@ a Shared Module that exports its resources:
   "name": "My Shared Module",
   <b>"export": {
     // Optional list of extension IDs explicitly allowed to
-    // import this Shared Module's resources.  If no whitelist
+    // import this Shared Module's resources.  If no allowlist
     // is given, all extensions are allowed to import it.
-    "whitelist": [
+    "allowlist": [
       "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
       "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
     ]
@@ -109,7 +109,7 @@ when needed by a dependent extension, and automatically uninstalled
 when the last extension which references it is uninstalled.  In order
 to upload an extension which uses a Shared Module, the Shared Module
 must be published in the Chrome Web Store and the extension must
-not be restricted from using the Shared Module by its whitelist.
+not be restricted from using the Shared Module by its allowlist.
 </p>
 
 <p>