insertCursor() {
    if (!this.showCursor) return;
    if (this.cursor) return;
    this.cursor = document.createElement('span');
    this.cursor.className = 'typed-cursor';
    this.cursor.setAttribute('aria-hidden', true);
    this.cursor.innerHTML = this.cursorChar;
    this.el.parentNode &&
      this.el.parentNode.insertBefore(this.cursor, this.el.nextSibling);
  }
On init, insert the cursor element
@private