libssh2_userauth_keyboard_interactive.3: fix man warning

It seemed to occur due to the excessive line length

docs/libssh2_userauth_keyboard_interactive.3

@@ -3,13 +3,12 @@
 libssh2_userauth_keyboard_interactive - convenience macro for \fIlibssh2_userauth_keyboard_interactive_ex(3)\fP calls
 .SH SYNOPSIS
 #include <libssh2.h>
+.nf
 
 int
 libssh2_userauth_keyboard_interactive(LIBSSH2_SESSION* session,
                                       const char *username,
-                                      LIBSSH2_USERAUTH_KBDINT_RESPONSE_FUNC((*response_callback)));
+           LIBSSH2_USERAUTH_KBDINT_RESPONSE_FUNC((*response_callback)));
-
-
 .SH DESCRIPTION
 This is a macro defined in a public libssh2 header file that is using the
 underlying function \fIlibssh2_userauth_keyboard_interactive_ex(3)\fP.