Make verify_dump off by default

It's a change of behaviour, so it should be off by default.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fio.1 b/fio.1
index 3b11122..aae7657 100644
--- a/fio.1
+++ b/fio.1
@@ -780,7 +780,7 @@
 .BI verify_dump \fR=\fPbool
 If set, dump the contents of both the original data block and the data block we
 read off disk to files. This allows later analysis to inspect just what kind of
-data corruption occurred. On by default.
+data corruption occurred. Off by default.
 .TP
 .BI verify_async \fR=\fPint
 Fio will normally verify IO inline from the submitting thread. This option