Bumping gaia.json for 6 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/a8d61d3a3da2
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #15746 from yzen/923139

Bug 923139 - making dialer app screen reader accessible.

========

https://hg.mozilla.org/integration/gaia-central/rev/f2d55468b697
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 923139 - fixed screen reader visibility of the suggestion overlay dialog.

========

https://hg.mozilla.org/integration/gaia-central/rev/a4fdd0785e50
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 923139 - updated call log to be selectable with the screen reader when not in edit mode and editable when in edit mode.

========

https://hg.mozilla.org/integration/gaia-central/rev/23d52b90c437
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 923139 - added button roles where necessary.

========

https://hg.mozilla.org/integration/gaia-central/rev/c1977bf161f9
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 923139 - added better support for disabled controls and disabling logic.

========

https://hg.mozilla.org/integration/gaia-central/rev/72d8564db60d
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 923139 - added aria labels and updated l10n where necessary.
Bumping manifests a=b2g-bump