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

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https://hg.mozilla.org/integration/gaia-central/rev/26b395d7a956
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #28809 from benoittgt/Bug_957224

Bug 957224 - Change sound notification duration r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/5b080b560796
Author: Benoit <benoit@hopsandfork.com>
Desc: Bug 957224 - Change sound notification duration r=etienne

Patch was made for the previous version :
https://bugzilla.mozilla.org/show_bug.cgi?id=957224
Add some tests to verify the 4000ms duration.

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "cef185cdc784c98255c0c68c89c7e1ca8a83a526", 
+        "git_revision": "a70946c84947d522d1fbb6c285e4de662020d7fb", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "51371becbe707e49d9247cc4740a8861de82a305", 
+    "revision": "26b395d7a956400c6487cb2e861b930fe0fb32c2", 
     "repo_path": "integration/gaia-central"
 }