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

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https://hg.mozilla.org/integration/gaia-central/rev/1c8dbc3d8e54
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #18575 from zacc/bug_999506

Bug 999506 - Detect the device_root before pushing/clearing files from t...

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https://hg.mozilla.org/integration/gaia-central/rev/97914924ceff
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 999506 - Detect the device_root before pushing/clearing files from the device, remove hardcoded references to /sdcard
Bumping manifests a=b2g-bump