docs: Don't mention full versions of 'linuxkit/kernel'
These get out of sync when doing a mechanic update of
kernel tags.
@@ -339,10 +339,10 @@ file:
```
kernel:
- image: linuxkit/kernel:4.9.66
+ image: linuxkit/kernel:4.9.<version>
cmdline: "console=tty0 console=ttyS0 console=ttyAMA0"
init:
- - <foo>/zfs-kmod:4.9.47
+ - <foo>/zfs-kmod:4.9.<version>
...
```
