Add Wx and Growl::GNTP to recommended modules.

Build.PL

@@ -21,6 +21,10 @@ my $build = Module::Build->new(
     build_requires => {
         'Test::More' => '0.10',
     },
+    recommends     => {
+        'Growl::GNTP' => '0.15',
+        'Wx'          => '0.9901',
+    },
     script_files    => ['slic3r.pl'],
 );
 $build->dispatch('installdeps');