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

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https://hg.mozilla.org/integration/gaia-central/rev/30c31f374af2
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #14027 from sashakruglov/music_application

migrate music app tests to app object

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https://hg.mozilla.org/integration/gaia-central/rev/72c1117d24a7
Author: Sasha Kruglov <sashakruglov@hotmail.com>
Desc: migrate music app tests to app object

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "8d1fddd00ccad26082e7e8eb3cf60c0ef43bd070", 
+    "revision": "30c31f374af27589c80d36e129ba2aa1fa5978f7", 
     "repo_path": "/integration/gaia-central"
 }