Fix wkhtmltopdf on macos (#300)

Author: arjunsuresh

script/get-wkhtmltopdf/meta.yaml

@@ -11,13 +11,15 @@ deps:
     skip_if_env:
       MLC_HOST_OS_TYPE:
         - windows
+  - tags: get,generic-sys-util,_wkhtmltopdf
+    enable_if_env:
+      MLC_HOST_OS_TYPE:
+        - darwin
 uid: 67ec874a3dfe4b87
 docker:
   pre_run_cmds:
     - mlc pull repo
 variations:
   with-qt:
     group: qt
-    default: true
-
-
+    default: true