add optional chaining

babel.config.js

@@ -2,4 +2,7 @@ module.exports = {
   presets: [
     '@babel/preset-env',
   ],
+  plugins: [
+    '@babel/plugin-proposal-optional-chaining',
+  ],
 }

docs/babel.config.js

@@ -3,4 +3,7 @@ module.exports = {
     '@babel/preset-env',
     '@babel/preset-react',
   ],
+  plugins: [
+    '@babel/plugin-proposal-optional-chaining',
+  ],
 }

docs/package.json

@@ -24,6 +24,7 @@
     "vue-github-button": "^1.1.2"
   },
   "devDependencies": {
+    "@babel/plugin-proposal-optional-chaining": "^7.11.0",
     "@babel/preset-env": "^7.11.5",
     "@babel/preset-react": "^7.10.4",
     "html-loader": "^1.3.1",

package.json

@@ -20,6 +20,7 @@
     "reset": "yarn clean:packages && rm -rf ./**/.cache && rm -rf ./**/node_modules && rm -rf ./yarn.lock && yarn install"
   },
   "devDependencies": {
+    "@babel/plugin-proposal-optional-chaining": "^7.11.0",
     "@babel/preset-env": "^7.11.5",
     "@types/prosemirror-commands": "^1.0.3",
     "@types/prosemirror-history": "^1.0.1",