strace.1: fix a typo

* strace.1: Fix a typo in example description.
This fixes Debian bug #653309.
diff --git a/strace.1 b/strace.1
index e01f3a4..8ca8593 100644
--- a/strace.1
+++ b/strace.1
@@ -181,7 +181,7 @@
 .CW
 open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3
 .CE
-Here the three argument form of open is decoded by breaking down the
+Here the third argument of open is decoded by breaking down the
 flag argument into its three bitwise-OR constituents and printing the
 mode value in octal by tradition.  Where traditional or native
 usage differs from ANSI or POSIX, the latter forms are preferred.