[contenthash] generated by this plugin does not match the hash generated by css-loader 5.2.0

Content hashes in css class names generated by this plugin are not the same as the hashes generated by `css-loader`.

Example:

`babel-plugin-react-css-module` => `navbar__container___2dO7z`
`css-loader` => `navbar__container___ocJ3d`

Debugging webpack reveals the reason - the `options.content` values used are different. Example (actual library name replaced by `xxx`):

`content` value used by `babel-plugin-react-css-module`:

```
node_modules/xxx/components/Navbar/navbar.scss+container
```

`content` value used by `css-loader`:

```
node_modules/frontier-pub/components/Navbar/navbar.scss[NIL]container
```

In the second value above, `[NIL]` is `\x00`

This `\x00` character is used in `css-loader/dist/utils.js` like this:

```js
options.content = `${options.hashPrefix}${relativeMatchResource}${relativeResourcePath}\x00${localName}`;
```

Versions:
* css-loader: 5.2.0
* babel-plugin-react-css-module: 5.2.6