Issue title: Bug: the text on image  sliders are synchronized
 Issue body: When you click  text `111` it should trigger `this.yoyo` but it triggers `this.yoyo2`.

When you click  text `222` it should trigger `this.yoyo2` but it triggers `this.yoyo`.

Strange bug~~ please fix it thank you.



    class App extends React.Component {

        yoyo() {
          console.log("111")
        }
        yoyo2() {
          console.log("222")
        }
        render() {

            var settings = {

            }

            return (
                  <Slider {...settings} className="slider-portal-container">
                    <div>
                      <h3　className="slider-portal-text" onClick={this.yoyo}>111</h3>
                      <img className="slider-portal-img" src="img/slides/slide_1.jpg" />
                    </div>

                    <div>
                      <h3　className="slider-portal-text" onClick={this.yoyo2}>222</h3>

                      <img className="slider-portal-img" src="img/slides/slide_2.jpg" />
                    </div>
                  </Slider>
            )
        }
    }


 Comments: 
 Comment 0: It could be problem with your css
{'source': 'GithubIssues', 'repo_name_with_owner': 'akiran/react-slick', 'issue_id': 170516670, 'repo_stars': 11238.0}