Tighten protected/public/const in shortcode PHP [LACE]

[nfreear]

Instead of:

<?php
class Evidence_Hub_Shortcode_Hypothesis_Sankey extends Evidence_Hub_Shortcode {

    public $shortcode = 'evidence_summary';
//...
    function content() {
//...

We do this:

<?php
class Evidence_Hub_Shortcode_Hypothesis_Sankey extends Evidence_Hub_Shortcode {

    const SHORTCODE = 'hypothesis_sankey';
//...
    protected function content() {
//...

[nfreear]

Complete, I think!