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

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https://hg.mozilla.org/integration/gaia-central/rev/e6c4a9eb4ba5
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #17683 from gasolin/issue--971538

Bug 971538 - [System2] Instantiable PermissionManager, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/2d960ba50df5
Author: gasolin <gasolin@gmail.com>
Desc: Bug 971538 - [System2] Instantiable PermissionManager

- rename currentPermission to permissionType
Bumping manifests a=b2g-bump