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

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https://hg.mozilla.org/integration/gaia-central/rev/745cc77244fc
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #12343 from lightsofapollo/marionette-vbump

vbump 0.15.5

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https://hg.mozilla.org/integration/gaia-central/rev/33ed527d4d6d
Author: James Lal <james@lightsofapollo.com>
Desc: vbump 0.15.5

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "8b2bd22d66c56b7f8c0cf0d504500077d9886467", 
+    "revision": "745cc77244fc62b35d395893a520cc36743648a3", 
     "repo_path": "/integration/gaia-central"
 }