_animateIndicator(prevIndex) {
      let leftDelay = 0,
        rightDelay = 0;

      if (this.index - prevIndex >= 0) {
        leftDelay = 90;
      } else {
        rightDelay = 90;
      }

      // Animate
      let animOptions = {
        targets: this._indicator,
        left: {
          value: this._calcLeftPos(this.$activeTabLink),
          delay: leftDelay
        },
        right: {
          value: this._calcRightPos(this.$activeTabLink),
          delay: rightDelay
        },
        duration: this.options.duration,
        easing: 'easeOutQuad'
      };
      anim.remove(this._indicator);
      anim(animOptions);
    }
Animates Indicator to active tab.
@param {Number} prevIndex