Docs: proc: fix kernel version

Change the kernel version in table 1-2 from 3.20 to 4.1
Signed-off-by: NChen Hanxiao <chenhanxiao@cn.fujitsu.com>
Reviewed-by: NNathan Scott <nathans@redhat.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/filesystems/proc.txt

@@ -205,7 +205,7 @@ asynchronous manner and the value may not be very precise. To see a precise
 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 It's slow but very precise.
 
-Table 1-2: Contents of the status files (as of 3.20.0)
+Table 1-2: Contents of the status files (as of 4.1)
 ..............................................................................
  Field                       Content
  Name                        filename of the executable