Bumping gaia.json for 4 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/e2101f7c2ece
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #13281 from MBRSL/bug-933571-keyboard

Bug 933571 - [HW test] iframe shows nothing in keyboard test, r=gasolin

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https://hg.mozilla.org/integration/gaia-central/rev/185c39b4e4b1
Author: Tom Jao <tjao@mozilla.com>
Desc: Bug 933571 - [HW test] iframe shows nothing in keyboard test

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https://hg.mozilla.org/integration/gaia-central/rev/cf175e3f1fd4
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #13280 from MBRSL/bug-931723-multiactivities

Bug 931723 - [HW test] multiactivities doesn't work, r=gasolin

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https://hg.mozilla.org/integration/gaia-central/rev/cd04ae548640
Author: Tom Jao <tjao@mozilla.com>
Desc: Bug 931723 - [HW test] multiactivities doesn't work

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "ad91f0092cb25284d4ed4fa88576a89e7e15c6bd", 
+    "revision": "e2101f7c2ecec55cad80f18b8c45271424e6bce4", 
     "repo_path": "/integration/gaia-central"
 }