proptypes changes impacted inferno-compat

inferno-compat expects `proptypes` to export `proptypes.default`. Can you please export both directly and using default property?

```
> require('proptypes').default
undefined

> require('proptypes')
{ array: { [Function: bound checkType] isRequired: [Function: bound checkType] },
bool: { [Function: bound checkType] isRequired: [Function: bound checkType] },
func: { [Function: bound checkType] isRequired: [Function: bound checkType] },
number: { [Function: bound checkType] isRequired: [Function: bound checkType] },
object: { [Function: bound checkType] isRequired: [Function: bound checkType] },
string: { [Function: bound checkType] isRequired: [Function: bound checkType] },
symbol: { [Function: bound checkType] isRequired: [Function: bound checkType] },
any: { [Function: bound checkType] isRequired: [Function: bound checkType] },
arrayOf: [Function: createArrayOfTypeChecker],
element: { [Function: bound checkType] isRequired: [Function: bound checkType] },
instanceOf: [Function: createInstanceTypeChecker],
node: { [Function: bound checkType] isRequired: [Function: bound checkType] },
objectOf: [Function: createObjectOfTypeChecker],
oneOf: [Function: createEnumTypeChecker],
oneOfType: [Function: createUnionTypeChecker],
shape: [Function: createShapeTypeChecker] }
```

從 proptypes 套件的進入點開始，檢查其目前的匯出是如何組成的。重現 issue 中所示的兩個 require 呼叫，然後驗證直接匯出和 .default 屬性是否都提供相同的 PropTypes API。

由索引模型根據 Issue 內容生成。