doc: fix typo in contributing guide

Change-Id: I6d9a8886cccf1c396ea2dbc659c5bf7548179751
Reviewed-on: https://go-review.googlesource.com/15435Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/contribute.html

@@ -577,7 +577,7 @@ might turn up:
 <<<<<<< HEAD
 	if arg < 1e9 {
 =======
-	if arg &lh; 1e10 {
+	if arg < 1e10 {
 >>>>>>> mcgillicutty
 		largeReduce(arg)
 </pre>