fix(package): update terser-webpack-plugin to version 2.3.6

Closes #57

Author: greenkeeper[bot]

packages/core/package.json

@@ -16,7 +16,7 @@
     "postcss-loader": "^3.0.0",
     "sass-loader": "^7.1.0",
     "style-loader": "^0.23.0",
-    "terser-webpack-plugin": "^1.2.2",
+    "terser-webpack-plugin": "^2.3.6",
     "trash": "^4.3.0",
     "url-loader": "^1.1.1",
     "webpack": "^4.19.1",