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#### Is your feature request related to a problem? Please describe.
While trying to migrate to the new FormData autogeneration (by using postForm or setting Content-Type to multipart) I realized arrays won't work anymore. An 'arr' proprety with two entries will be converted to name="arr.0" and name="arr.1" in the payload.
I saw in the source-code that once the name has a suffix like '[]' it will post it as such. But our springboot backend wants the key to be 'arr' (not 'arr[]') and our client-side typescript interface has a key named 'arr' and not 'arr[]' either.

#### Describe the solution you'd like
Plain arrays should also be send automatically, without the need to put '[]' to its name. If that's a breaking change, make it optional via options.

#### Describe alternatives you've considered
Springboot can't parse the default 'arr.0', 'arr.1' format. And adding '[]' to the type, the client-side object and the desired property in the backend is not an ideal solution.

In typescript properties of types/interfaces usually don't have a '[]' suffix. But the whole point of migrating to this new feature is to have type-safe services with a typed payload instead of just any 'FormData' object.

#### Additional context

lib/utils.js
str = String(str);
  if (position === undefined || position > str.length) {
    position = str.length;
  }
  position -= searchString.length;
  var lastIndex = str.indexOf(searchString, position);
  return lastIndex !== -1 && lastIndex === position;
}
/**
 * Returns new array from array like object
 * @param {*} [thing]
 * @returns {Array}
 */
function toArray(thing) {