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

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https://hg.mozilla.org/integration/gaia-central/rev/8b637bb5a1ec
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #31143 from KevinGrandon/bug_1188459_revert_smoketest_blocker_2

Revert "Bug 1186587 - Don't ensure() the homescreen for every Service.query('getHomescreen') r=kgrandon"

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https://hg.mozilla.org/integration/gaia-central/rev/84c6eec226bb
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Revert "Bug 1186587 - Don't ensure() the homescreen for every Service.query('getHomescreen') r=kgrandon"

This reverts commit 62d9420fc0915ab11ad5d23e105c929d4b5afae6.

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "494d8169d36ee497d3e2111c839382dde5ebaeba", 
+        "git_revision": "a317a3edc00eea564d39bd89d032a76546477cd7", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "dd53699bff645f26ee45d721da7b6852e2d71cfb", 
+    "revision": "8b637bb5a1eca258275a5847f2f522aa8ac6e5d4", 
     "repo_path": "integration/gaia-central"
 }