fixed skip_all problem in t/manifest

t/manifest.t

@@ -9,5 +9,5 @@ unless ( $ENV{RELEASE_TESTING} ) {
 }
 
 eval "use Test::CheckManifest 0.9";
-plan skip_al => "Test::CheckManifest 0.9 required" if $@;
+plan skip_all => "Test::CheckManifest 0.9 required" if $@;
 ok_manifest();