Update dependency autoprefixer to v9.8.6 (#16)

package.json

@@ -27,7 +27,7 @@
     "gulp-sass": "4.1.0",
     "gulp-postcss": "8.0.0",
     "cssnano": "4.1.10",
-    "autoprefixer": "9.8.5",
+    "autoprefixer": "9.8.6",
     "node-sass-tilde-importer": "^1.0.2"
   },
   "dependencies": {