fix(typings): fix type for angular 5

in issue BrasilAPI#112, we saw the problem with angular 5.

in my tests, i install angular 5 and rollback the definition without workarround
solved for default function microsoft/TypeScript#5073

and this back work, i think this worked because typescript can have a fix in recent version.

README.md

@@ -171,10 +171,10 @@ require('/dist/cep-promise-browser.min.js')
   }
 ```
 
-#### Angular 2
+#### Angular 2/4/5
 
 ``` ts
-import * as cep from 'cep-promise'
+import cep from 'cep-promise'
 
 cep('05010000')
   .then(console.log)

index.d.ts

@@ -7,12 +7,5 @@ declare module 'cep-promise' {
     neighborhood: string
   }
 
-  // this workarround is because this : https://github.com/Microsoft/TypeScript/issues/5073
-  namespace cep {}
-
-  function cep( cep: string | number ): Promise<CEP>
-
-  export = cep
+  export default function cep(cep: string | number): Promise<CEP>
 }
-
-