Fixed a config docs typo.

redis.conf

@@ -279,7 +279,7 @@ appendonly no
 #
 # The default is "everysec" that's usually the right compromise between
 # speed and data safety. It's up to you to understand if you can relax this to
-# "no" that will will let the operating system flush the output buffer when
+# "no" that will let the operating system flush the output buffer when
 # it wants, for better performances (but if you can live with the idea of
 # some data loss consider the default persistence mode that's snapshotting),
 # or on the contrary, use "always" that's very slow but a bit safer than