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

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https://hg.mozilla.org/integration/gaia-central/rev/20b7d51bd03d
Author: Dale  Harvey <dale@arandomurl.com>
Desc: Merge pull request #10702 from benfrancis/796565

Bug 796565 - Share URL of web page - browser part. r=daleharvey

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https://hg.mozilla.org/integration/gaia-central/rev/72758617318e
Author: Ben Francis <ben@tola.me.uk>
Desc: Bug 796565 - Share URL of web page - browser part

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "7fa372bfb15c8d8f1ad22d70af111bbe3a9adeef", 
+    "revision": "20b7d51bd03d385e816b49d6c4b86b8cd59a97fd", 
     "repo_path": "/integration/gaia-central"
 }