Support for dictionary

It is not possible to configure models where keys start with numbers
```json
"Section": {
    "123": 321,
    "234": 432
}
```

I tried adding the dictionary directly, but it didn't help either:
```cs
MockConfiguration
	.SetupConfiguration()
	.Returns(new
	{
		Section  = new Dictionary<string, int>
		{
			{ "123", 321 },
			{ "234", 432 }
		}
	});
```

Need support for it!!!