TypeError: Cannot read property 'transformFile' of undefined

**Versions**:

"react-native": "0.59.10",
"react-native-obfuscating-transformer": "^1.0.0",

**Files**:

metro.config.js:

```js
module.exports = {
transformer: {
babelTransformerPath: require.resolve("./transformer"),
getTransformOptions: async () => ({
transform: {
experimentalImportSupport: false,
inlineRequires: false,
},
}),
},
};
```

transformer.js:

```js
const obfuscatingTransformer = require('react-native-obfuscating-transformer')

module.exports = obfuscatingTransformer({})
```

**Error I am getting:**

```sh
Loading dependency graph, done.
Loading dependency graph...error Cannot read property 'transformFile' of undefined
debug TypeError: Cannot read property 'transformFile' of undefined
at /home/chris/Documents/JSObfuscation/ObfuscationTest/node_modules/metro/src/Bundler.js:83:34
at Generator.next ()
at asyncGeneratorStep (/home/chris/Documents/JSObfuscation/ObfuscationTest/node_modules/metro/src/Bundler.js:14:24)
at _next (/home/chris/Documents/JSObfuscation/ObfuscationTest/node_modules/metro/src/Bundler.js:34:9)
```

**Repo**

Simplest repo I could make that reproduces this error:

[https://github.com/ExoMemphiz/ObfuscationTest/](https://github.com/ExoMemphiz/ObfuscationTest/)

使用链接的 ObfuscationTest 复现，并从 metro.config.js 和 transformer.js 开始。结合 node_modules/metro/src/Bundler.js:83 检查 transformer 入口点，以确定 transformFile 为何不可用，然后验证在 React Native 0.59.10 上依赖图能够在没有此错误的情况下加载。

由索引模型根据 Issue 内容生成。