Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/5599c50ef6bc
Author: Mike Pennisi <mike@mikepennisi.com>
Desc: Bug 972526 - [clock] Integration tests' Stopwatch abstraction hides a race condition

r=mcav

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "b62d4e94b361dfe4d0141263940ad5ce675b44c5", 
+    "revision": "5599c50ef6bc4f47dc77698dc74b2607e2c0722a", 
     "repo_path": "/integration/gaia-central"
 }