Bump terser from 4.8.0 to 5.3.1

Bumps [terser](https://github.com/terser/terser) from 4.8.0 to 5.3.1.
- [Release notes](https://github.com/terser/terser/releases)
- [Changelog](https://github.com/terser/terser/blob/master/CHANGELOG.md)
- [Commits](terser/terser@v4.8.0...v5.3.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -52,7 +52,7 @@
     "karma-coverage": "^2.0.1",
     "karma-qunit": "^4.0.0",
     "qunit": "^2.9.2",
-    "terser": "^4.1.2",
+    "terser": "^5.3.1",
     "uglifyjs-webpack-plugin": "^2.0.1",
     "webpack": "^4.20.2",
     "webpack-cli": "^3.1.1"