test: uncomment the airbnb eslint migrator test

Author: haoqunjiang

packages/@vue/cli-plugin-eslint/__tests__/eslintMigrator.spec.js

@@ -33,8 +33,7 @@ test('upgrade: should add eslint to devDependencies', async () => {
   expect(updatedPkg.devDependencies.eslint).toMatch('^4')
 })
 
-// skip this test case until we fixed test caching issue
-test.skip('upgrade: should upgrade eslint from v5 to v6', async () => {
+test('upgrade: should upgrade eslint from v5 to v6', async () => {
   const project = await create('plugin-eslint-with-eslint-5', {
     plugins: {
       '@vue/cli-plugin-eslint': {