fix(module): switch to commonjs2 libraryTarget (#379)

Emit `__esModule` indicators for ES modules to distinguish between
them and CommonJS modules.

If libraryTarget is set to `commonjs`, the bundle does not match the interface
provided by the type declarations because `default` imports end up as
`module.exports`, e.g.:

```
import transformer from 'ts-auto-mock/transformer'; // commonjs -> { default: [Function (anonymous)] }
import transformer from 'ts-auto-mock/transformer'; // commonjs2 -> [Function (anonymous)] ✓
```

Co-authored-by: Vittorio Guerriero <[email protected]>

config/modules/base/webpack.base.js

@@ -26,7 +26,7 @@ module.exports = (options) => {
             ]
         },
         output: {
-            libraryTarget: "commonjs",
+            libraryTarget: "commonjs2",
             filename: "[name].js"
         },
         plugins: [