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

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https://hg.mozilla.org/integration/gaia-central/rev/66fdc19a47de
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #13243 from TheoChevalier/bug-868345

Bug 868345 - [system] 'What's in a crash report?' shown after crash not ...

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https://hg.mozilla.org/integration/gaia-central/rev/74123faffc99
Author: TheoChevalier <theo.chevalier11@gmail.com>
Desc: Bug 868345 - [system] 'What's in a crash report?' shown after crash not scrollable

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "2304e5bee7ee75ea9dc3ac49d1a30cad847e926e", 
+    "revision": "66fdc19a47de99173cfd098774f1ea1d4a856dc3", 
     "repo_path": "/integration/gaia-central"
 }