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

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https://hg.mozilla.org/integration/gaia-central/rev/7cc2b1b29122
Author: Germán Toro del Valle <gtorodelvalle@gmail.com>
Desc: Merge pull request #26874 from gtorodelvalle/dialer-bug-911055-dmtf-tones-with-pauses

Bug 911055 - [Dialer]DuT doesn allow to dial a <<pause>>

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https://hg.mozilla.org/integration/gaia-central/rev/9ff60cb591f0
Author: German Toro del Valle <gtorodelvalle@gmail.com>
Desc: Bug 911055 - [Dialer]DuT doesn allow to dial a <<pause>>

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https://hg.mozilla.org/integration/gaia-central/rev/e561906d9c19
Author: Fernando Jiménez Moreno <ferjmoreno@gmail.com>
Desc: Merge pull request #27065 from ferjm/overlay

Bug 1101029 - Overlay iframe on top of front-most app. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/20ad248a5473
Author: Fernando Jiménez Moreno <ferjmoreno@gmail.com>
Desc: Bug 1101029 - Overlay iframe on top of front-most app. r=alive

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "dd880ed18da47b3bc5b28188693c7ed7433ae013", 
+    "revision": "7cc2b1b29122f6a5eef9a8ae47991253a2571c0f", 
     "repo_path": "integration/gaia-central"
 }