antora upgrade

Author: jayachristina

package.json

@@ -8,8 +8,8 @@
     "url": "https://twitter.com/@kamesh_sampath"
   },
   "dependencies": {
-    "@antora/cli": "^2.3.1",
-    "@antora/site-generator-default": "^2.3.1",
+    "@antora/cli": "^3.1",
+    "@antora/site-generator-default": "^3.1",
     "@babel/cli": "^7.5.5",
     "@babel/core": "^7.5.5",
     "@babel/polyfill": "^7.4.4",