chore: add autoprefixer to devDependencies

Author: bpzhang

package.json

@@ -78,6 +78,7 @@
     "@vue/cli-plugin-unit-jest": "3.5.3",
     "@vue/cli-service": "3.5.3",
     "@vue/test-utils": "1.0.0-beta.29",
+    "autoprefixer": "^9.5.1",
     "babel-core": "7.0.0-bridge.0",
     "babel-eslint": "10.0.1",
     "babel-jest": "23.6.0",