Downgrade mocha and fix test issue

package.json

@@ -14,7 +14,7 @@
     "wait": "rimraf dist && wait-on http://localhost:3000/dist/ffmpeg.dev.js",
     "test": "npm-run-all -p -r start test:all",
     "test:all": "npm-run-all wait test:browser:ffmpeg test:node:all",
-    "test:node": "nyc mocha --exit --bail --require ./scripts/test-helper.js",
+    "test:node": "NODE_OPTIONS=--experimental-worker nyc mocha --exit --bail --require ./scripts/test-helper.js",
     "test:node:all": "npm run test:node -- ./tests/*.test.js",
     "test:browser": "mocha-headless-chrome -a incognito -a no-sandbox -a disable-setuid-sandbox -a disable-logging -t 300000",
     "test:browser:ffmpeg": "npm run test:browser -- -f ./tests/ffmpeg.test.html"
@@ -46,26 +46,26 @@
     "is-electron": "^2.2.0",
     "is-url": "^1.2.4",
     "node-fetch": "^2.6.0",
-    "regenerator-runtime": "^0.13.3",
+    "regenerator-runtime": "^0.13.5",
     "resolve-url": "^0.2.1"
   },
   "devDependencies": {
-    "@babel/core": "^7.6.4",
-    "@babel/preset-env": "^7.6.3",
-    "babel-loader": "^8.0.6",
+    "@babel/core": "^7.9.0",
+    "@babel/preset-env": "^7.9.0",
+    "babel-loader": "^8.1.0",
     "cors": "^2.8.5",
-    "eslint": "^6.1.0",
-    "eslint-config-airbnb-base": "^14.0.0",
-    "eslint-plugin-import": "^2.18.2",
+    "eslint": "^6.8.0",
+    "eslint-config-airbnb-base": "^14.1.0",
+    "eslint-plugin-import": "^2.20.1",
     "expect.js": "^0.3.1",
     "express": "^4.17.1",
-    "mocha": "^6.2.2",
+    "mocha": "^5.2.0",
     "mocha-headless-chrome": "^2.0.3",
     "npm-run-all": "^4.1.5",
     "nyc": "^14.1.1",
     "wait-on": "^3.3.0",
-    "webpack": "^4.41.2",
-    "webpack-cli": "^3.3.9",
+    "webpack": "^4.42.0",
+    "webpack-cli": "^3.3.11",
     "webpack-dev-middleware": "^3.7.2"
   }
 }