fix sliders when editing code

glsl/raymarching.js

  editor.visible = true;
  editor.el = document.createElement("textarea");
  editor.el.id = "editor";
  editor.el.value = fragmentShaderSrc;
  editor.el.value = tt.fragmentShaderSrc;
  document.body.appendChild(editor.el);
  
  editor.el.onkeydown = function(ev) {
        tt = TwoTriangles(canvas, editor.el.value);
        sidebarEl.innerHTML = "";
        sliders = findSliders(fragmentShaderSrc);
        sliders = findSliders(tt.fragmentShaderSrc);
        initSliders(tt.gl, tt.program, sliders, function(ev) {
          requestAnimationFrame(tt.render);
        });