Test types (#4140)

* Distinguish request and response data types

* Fix Axios headers type

`axios.headers` is not of the same type as `request.headers`, so a new type
`AxiosDefaults` was introduced

* Replace grunt-ts with dtslint

This asserts that the type definitions are valid in the specified TypeScript
version and above. This is the same tool that is used by DefinitelyTyped.

* Remove grunt-ts

* Restore typescript dependency

* Fix missing semicolons

Co-authored-by: Claas Augner <github@caugner.de>
Co-authored-by: Jay <jasonsaayman@gmail.com>

test/typescript/axios.ts

@@ -8,7 +8,7 @@ import axios, {
   CancelToken,
   CancelTokenSource,
   Canceler
-} from '../../';
+} from 'axios';
 
 const config: AxiosRequestConfig = {
   url: '/user',
@@ -170,8 +170,8 @@ axios.patch<User>('/user', { name: 'foo', id: 1 })
 // (Typed methods) with custom response type
 
 const handleStringResponse = (response: string) => {
-  console.log(response)
-}
+  console.log(response);
+};
 
 axios.get<User, string>('/user?id=12345')
   .then(handleStringResponse)
@@ -342,11 +342,11 @@ axios.get('/user')
 
 axios.get('/user')
   .catch((error: any) => 'foo')
-  .then((value: string) => {});
+  .then((value) => {});
 
 axios.get('/user')
   .catch((error: any) => Promise.resolve('foo'))
-  .then((value: string) => {});
+  .then((value) => {});
 
 // Cancellation