configure: bumb required alsa-lib version to 1.2.13

Code requires new sequencer API extensions.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

configure.ac

@@ -21,7 +21,7 @@ AC_PROG_SED
 AC_DISABLE_STATIC
 AM_PROG_LIBTOOL
 PKG_PROG_PKG_CONFIG
-AM_PATH_ALSA(1.2.12)
+AM_PATH_ALSA(1.2.13)
 if test "x$enable_alsatest" = "xyes"; then
 AC_CHECK_FUNC([snd_ctl_elem_add_enumerated],
 	      , [AC_ERROR([No user enum control support in alsa-lib])])