Documentation/filesystems/proc.txt: indentation fix

Signed-off-by: Adrian Bunk <bunk@stusta.de>

Documentation/filesystems/proc.txt

@@ -418,7 +418,7 @@ VmallocChunk:   111088 kB
        Dirty: Memory which is waiting to get written back to the disk
    Writeback: Memory which is actively being written back to the disk
       Mapped: files which have been mmaped, such as libraries
-              Slab: in-kernel data structures cache
+        Slab: in-kernel data structures cache
  CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
               this is the total amount of  memory currently available to
               be allocated on the system. This limit is only adhered to