Bumping gaia.json for 2 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/911756823e45
Author: John Ford <john@johnford.info>
Desc: Merge pull request #10932 from brendandahl/pdfjs-v0.8.326

Bug 892721 - Update gaia pdf.js to version 0.8.326.

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https://hg.mozilla.org/integration/gaia-central/rev/4631d9e630a8
Author: Brendan Dahl <brendan.dahl@gmail.com>
Desc: Bug 892721 - Update gaia pdf.js to version 0.8.326.

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "846f8e7089361d42e1362ab591561f94d3bd31e9", 
+    "revision": "911756823e4537d9be0df3b18634398f2a41e39c", 
     "repo_path": "/integration/gaia-central"
 }