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

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https://hg.mozilla.org/integration/gaia-central/rev/86988321a865
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #30589 from gasolin/issue-1173675-system

Bug 1173675 - link gaia jsdoc gh-page on system readme, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/2017cb9f7b33
Author: gasolin <gasolin@gmail.com>
Desc: Bug 1173675 - link gaia jsdoc gh-page on system readme, r=alive

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "f8a1a15d8e98b0316e8e89682bab9460838fdeed", 
+        "git_revision": "720e38c5140272ea38fcedc142b4395e443632c7", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "bb241ae4e33ade6338e0ce84dacaf26235177959", 
+    "revision": "86988321a865a0ce7668da478ebfce8fdc9b01e0", 
     "repo_path": "integration/gaia-central"
 }