Make the default type of response data never (#3002)

This requires TypeScript users to explicitly define the type of the data they
are consuming.

Before this, data was `any` by default. This means TypeScript consumers didn’t
get type safety if they forgot to specify the type.

Technically this is a breaking change for TypeScript users, as this will report
errors if they forgot to specifiy the response type. The simplest workaround
would be to explicitly set the response type to `any`, so it’s not breaking
much.

The `unknown` type is probably a slightly better fit, but this requires
TypeScript ^3.

`data` is still `any` in the very specific use case mentioned in
https://github.com/microsoft/TypeScript/issues/38969

Co-authored-by: Jay <jasonsaayman@gmail.com>

test/typescript/axios.ts

@@ -296,7 +296,7 @@ axios.interceptors.response.use((response: AxiosResponse) => Promise.resolve(res
 // Adapters
 
 const adapter: AxiosAdapter = (config: AxiosRequestConfig) => {
-  const response: AxiosResponse = {
+  const response: AxiosResponse<any> = {
     data: { foo: 'bar' },
     status: 200,
     statusText: 'OK',