test: force exit tests execution for webpack 4

Author: freddy38510

package.json

@@ -15,7 +15,7 @@
     "pretest": "tsc",
     "test": "jest",
     "pretest:webpack4": "tsc",
-    "test:webpack4": "WEBPACK4=true jest",
+    "test:webpack4": "WEBPACK4=true jest --forceExit",
     "dev-example": "node example/devServer.js --config example/webpack.config.js --inline --hot",
     "build-example": "rm -rf example/dist && webpack --config example/webpack.config.js --env.prod",
     "build-example-ssr": "rm -rf example/dist-ssr && webpack --config example/webpack.config.js --env.prod --env.ssr && node example/ssr.js",