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

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https://hg.mozilla.org/integration/gaia-central/rev/59cd7c4ee453
Author: Salvador de la Puente González <salva@unoyunodiez.com>
Desc: Merge pull request #13552 from lodr/bug-912510-non-zero-values

Bug 912510 - Removing non zero placeholders

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https://hg.mozilla.org/integration/gaia-central/rev/31c942c4e450
Author: lodr <salva@unoyunodiez.com>
Desc: Bug 912510 - Removing non zero placeholders

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "6c916d22a128d43da8098defa5154934213d5aff", 
+    "revision": "59cd7c4ee45334b96000b37f4948e209a75d8b6c", 
     "repo_path": "/integration/gaia-central"
 }