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

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https://hg.mozilla.org/integration/gaia-central/rev/13bba6b63383
Author: RickyChien <ricky060709@gmail.com>
Desc: Merge pull request #18615 from RickyChien/bug-998757-follow-up

Bug 998776 - Follow-up, update gaia_node_modules.revision r=me

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https://hg.mozilla.org/integration/gaia-central/rev/447b4e51a0f8
Author: Ricky Chien <ricky060709@gmail.com>
Desc: Bug 998776 - Follow-up, update gaia_node_modules.revision

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https://hg.mozilla.org/integration/gaia-central/rev/263342b90317
Author: RickyChien <ricky060709@gmail.com>
Desc: Merge pull request #18511 from RickyChien/bug-998776

Bug 998776 - [Follow up of Bug 991446] Fix the broken coverage result on console r=@yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/55e330a9bd3a
Author: Ricky Chien <ricky060709@gmail.com>
Desc: Bug 998776 - [Follow up of Bug 991446] Fix the broken coverage result on console

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "c9da1e12a2e8b319080cf41acc2ce3d429468d76", 
+    "revision": "13bba6b63383add2deb1aa9f173c695928681882", 
     "repo_path": "/integration/gaia-central"
 }