setjmp.3: wfix

Reported-by: Stephan Bergmann <sbergman@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/setjmp.3

@@ -310,7 +310,7 @@ such as the steps equivalent to
 that occur upon a return from the initial call to
 .IR main ()),
 the behavior is undefined if the program subsequently makes a call to
-a non-async-signal-safe.
+a non-async-signal-safe function.
 The only way of avoiding undefined behavior is to ensure one of the following:
 .IP * 3
 After long jumping from the signal handler,