fix: support pug 3 (#254)

Author: df-pkennedy

package.json

@@ -25,7 +25,7 @@
   },
   "peerDependencies": {
     "gm": "^1.23.0",
-    "pug": "^2.0.0",
+    "pug": "^2.0.0 || ^3.0.0",
     "sharp": "^0.21.0",
     "vue": "^2.7.2",
     "vuetify": "^1.3.0 || ^2.0.0",