Bumping gaia.json for 6 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/54c9ca64aa49
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #13423 from AndreiH/bug935428

Bug 935428 - Mark test_geolocation_prompt.py as expected fail

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https://hg.mozilla.org/integration/gaia-central/rev/badbc86c3be6
Author: Andrei Hutusoru <andreihutusoru@P5069.(none)>
Desc: Bug 935428 - Mark test_geolocation_prompt.py as expected fail

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https://hg.mozilla.org/integration/gaia-central/rev/3b61b3a852e3
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #13426 from zacc/bug_935444

bug 935444 - Python, bolster wait for call screen to have loaded r=Bebe ...

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https://hg.mozilla.org/integration/gaia-central/rev/e7b8904328ca
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: bug 935444 - Python, bolster wait for call screen to have loaded r=Bebe r=Andreih

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https://hg.mozilla.org/integration/gaia-central/rev/a4be789913f4
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #13427 from julienw/935441-fix-keyboard-unit-tests

Bug 935441 - [Keyboard] 2 unit tests failures with the latest firefox bu...

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https://hg.mozilla.org/integration/gaia-central/rev/5413cf5ae17e
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 935441 - [Keyboard] 2 unit tests failures with the latest firefox builds r=janjongboom

Defines the property on `window` itself.

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "18667a9b93eaccd93d7f1fa681e4e32aa63405a3", 
+    "revision": "54c9ca64aa49bd72dd3a3226177282dcb23e7550", 
     "repo_path": "/integration/gaia-central"
 }