Fix the 'distclean' target.

Generated documentation needs to be removed by this target
for 'distcheck' to succeed.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
diff --git a/doc/Makefile.am b/doc/Makefile.am
index 67703e9..54ec270 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -38,5 +38,5 @@
 
 EXTRA_DIST = Doxyfile.in Makefile.lite doxygen.footer.html doxygen.header.html $(doc_DATA)
 
-maintainer-clean-local:
+distclean-local:
 	rm -rf FLAC.tag html/api doxytmp