Upgrade yarn

Author: cham11ng

package.json

@@ -15,8 +15,8 @@
  "chart.js": "^1.1.1",
  "cross-env": "^5.1",
  "font-awesome": "^4.7.0",
- "laravel-mix": "^2.0",
  "jquery": "^3.2",
+ "laravel-mix": "^2.0",
  "lodash": "^4.17.4",
  "metismenu": "^2.7.0",
  "popper.js": "^1.12",