fix(package): update terser-webpack-plugin to version 1.2.1

Closes #50

Author: greenkeeper[bot]

package.json

@@ -59,7 +59,7 @@
     "stylelint-config-styled-components": "0.1.1",
     "stylelint-processor-styled-components": "1.5.1",
     "stylelint": "9.8.0",
-    "terser-webpack-plugin": "1.1.0",
+    "terser-webpack-plugin": "1.2.1",
     "url-loader": "1.1.2",
     "webpack-dev-server": "3.1.10",
     "webpack-manifest-plugin": "2.0.4",