Fix POD formating

--- lib/Imager/Graph/Horizontal.pm
+++ lib/Imager/Graph/Horizontal.pm
@@ -580,8 +580,6 @@ sub _add_data_series {
   return;
 }
 
-=over
-
 =item show_vertical_gridlines()
 
 Shows vertical gridlines at the y-tics.
@@ -906,5 +904,8 @@ sub _composite {
   return ( $self->SUPER::_composite(), "graph", "vgrid" );
 }
 
+=back
+=cut
+
 1;
 
--- lib/Imager/Graph/Vertical.pm
+++ lib/Imager/Graph/Vertical.pm
@@ -1425,4 +1425,7 @@ sub _composite {
   return ( $self->SUPER::_composite(), "graph", "hgrid" );
 }
 
+=back
+=cut
+
 1;