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

========

https://hg.mozilla.org/integration/gaia-central/rev/6a8c178c6174
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #15009 from zacc/bug_949897

Bug 949897 - Investigate intermittents in test_cards_view_kill_apps_with_two_apps - Reenable test

========

https://hg.mozilla.org/integration/gaia-central/rev/7d6d996662f6
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 949897 - Investigate intermittents in test_cards_view_kill_apps_with_two_apps - Reenable test

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "5d371ef610e042d00bfcb13878d8a56210eec036", 
+    "revision": "6a8c178c617445f6a5b135129f6e8d47f64a4da0", 
     "repo_path": "/integration/gaia-central"
 }