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

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https://hg.mozilla.org/integration/gaia-central/rev/721762333dd7
Author: Borja Salguero <borjasalguero@users.noreply.github.com>
Desc: Merge pull request #13905 from borjasalguero/shield_callback_code

Bug 941597 - [Regression] Error when using activity from contacts r=juli...

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https://hg.mozilla.org/integration/gaia-central/rev/b5a6fbdc6a09
Author: borjasalguero <fbsc@tid.es>
Desc: Bug 941597 - [Regression] Error when using activity from contacts r=julienw

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "ae263cdfa1ca27cc8b08be2c4b6ffab640080d98", 
+    "revision": "721762333dd7d0f1cc14a29167a6c20af6f9f0a5", 
     "repo_path": "/integration/gaia-central"
 }