RCU documentation: Correct the name of a reference

Trying to go through the history of RCU (not for the weak
minded) led me to search for a non-existent paper.

Correct it to the actual reference

Signed-off-by: Dhaval Giani <dhaval.giani@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>

Index: linux/Documentation/RCU/RTFP.txt
===================================================================
--- linux.orig/Documentation/RCU/RTFP.txt
+++ linux/Documentation/RCU/RTFP.txt
@@ -186,7 +186,7 @@ Bibtex Entries
 
 @article{Kung80
 ,author="H. T. Kung and Q. Lehman"
-,title="Concurrent Maintenance of Binary Search Trees"
+,title="Concurrent Manipulation of Binary Search Trees"
 ,Year="1980"
 ,Month="September"
 ,journal="ACM Transactions on Database Systems"