Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/2571d5dffca8
Author: Min-Zhong "John" Lu <mnjul@users.noreply.github.com>
Desc: Merge pull request #20213 from mnjul/bug_1021860_lockscreen_icon_wrong_color

Bug 1021860 - [VsD Refresh] Lockscreen Visual Refresh > Lockscreen icons are not the right color  [r=gweng]

========

https://hg.mozilla.org/integration/gaia-central/rev/7c13fbdf52a0
Author: John Lu [:mnjul] <jlu@mozilla.com>
Desc: Bug 1021860 - [VsD Refresh] Lockscreen Visual Refresh > Lockscreen icons are not the right color

========

https://hg.mozilla.org/integration/gaia-central/rev/1d1603dd2d12
Author: Min-Zhong "John" Lu <mnjul@users.noreply.github.com>
Desc: Merge pull request #20211 from mnjul/bug_1021391_lockscr_unlock_icon_too_low

Bug 1021391 - [VsD Refresh] Lockscreen Visual Refresh > Unlock icon too low [r=gweng]

========

https://hg.mozilla.org/integration/gaia-central/rev/288ce7246a33
Author: John Lu [:mnjul] <jlu@mozilla.com>
Desc: Bug 1021391 - [VsD Refresh] Lockscreen Visual Refresh > Unlock icon too low
Bumping manifests a=b2g-bump