RELEASES.md: update release1.2 status
RELEASES.md: update release1.2 status

Signed-off-by: Wei Fu <df4176d36abdc6fd0d966de5d5471522668de494@gmail.com>

vdemeester/containerd,mikebrow/containerd,thaJeztah/containerd,estesp/containerd,dmcgowan/containerd,dmcgowan/containerd,mikebrow/containerd,containerd/containerd,containerd/containerd,vdemeester/containerd,crosbymichael/containerd,estesp/containerd,crosbymichael/containerd,thaJeztah/containerd