#### Is your feature request related to a problem? Please describe.
I want to use new toFormData method, but it is not typed in index.d.ts

#### Describe the solution you'd like
Add types for toFormData

#### Describe alternatives you've considered
Use ts-ignore

#### Additional context
None

test/typescript/axios.ts
import axios, {
  AxiosRequestConfig,
  AxiosResponse,
  AxiosError,
  AxiosInstance,
  AxiosAdapter,
  Cancel,
  CancelToken,
  CancelTokenSource,
  Canceler