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

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https://hg.mozilla.org/integration/gaia-central/rev/4a5a2ee1fd7e
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #21706 from etiennesegonzac/bug-1029979

Bug 1029979 - TonePlayer: prevent successive trash/ensureAudio() calls from creating an AudioContext with a null channel r=gsvelto

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https://hg.mozilla.org/integration/gaia-central/rev/dd33ea3cda66
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 1029979 - TonePlayer: prevent successive trash/ensureAudio() calls from creating an AudioContext with a null channel r=gsvelto
Bumping manifests a=b2g-bump