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

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https://hg.mozilla.org/integration/gaia-central/rev/27d21143813f
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #12856 from Neeraj-Seth/bug-890207_cursor_hide_issue

Bug 890207 - [B2G][Gaia][Keyboard][Auto-correction] If a wording include...

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https://hg.mozilla.org/integration/gaia-central/rev/e8c6bd452789
Author: Neeraj Kumar <neeraj_kumar@hcl.com>
Desc: Bug 890207 - [B2G][Gaia][Keyboard][Auto-correction] If a wording include special characters then moving the cursor to the end of a line, the cursor will disappear
Bug 915729 - Add mixed HWC and GPU Composition. r=ncameron, r=dwilson
Bug 920654 - Enable plane alpha support for HWC layers in newer H/W Composer. r=mwu, r=dwilson
Bug 927201 - Add null check before trying to close observer service. r=mrbkap
Bug 926553 - Reduce the number of items in test_arrays.html to avoid timeouts indebug B2G emulators. r=ehsan