[Docs][Stimulus] use camelCase for target naming

[Jibbarth]

Q	A
Bug fix?	no
New feature?	no
Issues	Fix #...
License	MIT

Hello!

I had some trouble following the doc for use stimulus_target and how to use them inside my stimulus controller.

As we can see on the stimulus target doc, the value of target should be in camelCase as it's mapped in property in the controller.

IE

<div data-my-controller-target="myElement">

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  static targets = [ "myElement"]
  // …
  foo() {
	this.myElementTarget.innerHTML = "...";
  }
}

So in this PR, I changed examples for stimulus_target usage.

[kbond]

Thank you Jibé.