Incompatibilidade com versões mais novas do Typescript

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used [patch-package](https://github.com/ds300/patch-package) to patch `cep-promise@4.1.2` for the project I'm working on.

Na versão 4.5.5 do Typescript, ao importar o módulo (ES6), ele resolve para 'any' por conta do "namespace cep {}".
Ao remover, ele volta a funcionar normalmente.

Here is the diff that solved my problem:

```diff
diff --git a/node_modules/cep-promise/index.d.ts b/node_modules/cep-promise/index.d.ts
index 6dfcf59..147230a 100644
--- a/node_modules/cep-promise/index.d.ts
+++ b/node_modules/cep-promise/index.d.ts
@@ -8,9 +8,6 @@ declare module 'cep-promise' {
service: string
}

- // this workarround is because this : https://github.com/Microsoft/TypeScript/issues/5073
- namespace cep {}
-
type AvaliableProviders =
"brasilapi" |
"correios" |
```

This issue body was [partially generated by patch-package](https://github.com/ds300/patch-package/issues/296).