gid 31 permission for /proc access

sys/kernel/initramfs-tools/ympbuild

@@ -33,7 +33,7 @@ prepare(){
     patch -Np1 -i ../non-debian.patch
     patch -Np1 -i ../no-dracut.patch
     # hidepid=2 default
-    sed -i "s/ proc \/proc/,hidepid=2&/g" init
+    sed -i "s/ proc \/proc/,hidepid=2,gid=31&/g" init
     # replace linux-version command
     sed -i "s/linux-version/false/g" hook-functions
     sed -i "s/linux-version list/ls \/lib\/modules\//g" update-initramfs