tabが上手く反映されない。

HTML
1<!doctype html>
2<html lang="ja">
3  <head>
4    <!-- Required meta tags -->
5    <meta charset="utf-8">
6    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
7
8    <!-- Bootstrap CSS -->
9    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
10    <link rel="stylesheet" href="css/style.css">
11    <title>Dotinstall App</title>
12
13    <style>
14      .cover{
15        background: url(img/bg.png);
16        background-size: cover;
17      }
18    </style>
19  </head>
20  <body>
21    <!--
22      [p/m][location]-[size]
23
24      location
25      - t, b, l, r
26     - x（上下）, y（左右）
27
28      size
29      - 0
30      - 1: 0.25rem
31      - 2: 0.5rem
32      - 3: 1.0rem
33      - 4: 1.5rem
34      - 5: 3.0rem
35      - auto
36  -->
37  <!--
38  bootstrapの４つのブレイクポイント
39  レスポンシブ用
40  ・576px and up: sm  （576px以上）
41  ・768px and up: md
42  ・992px and up: lg
43  ・1200px and up: xl
44-->
45    <header>
46    <div class="cover text-white text-center py-5">
47      <h1 class="display-4 md-4 ">Dotinstall App</h1>
48      <a href="#" class="btn btn-primary btn-lg">Get It Now!</a>
49    </div>
50    </header>
51
52    <main>
53      <section class="py-5">
54        <h2 class="text-center mb-5">Features</h2>
55
56        <div class="container">
57          <div class="mb-5 row">
58            <div class="col-sm-8">
59              <h3>Awesome</h3>
60              <p>Hello. Hello. Hello. Hello. Hello. Hello. Hello.
61              Hello. Hello. Hello. Hello. Hello. Hello. </p>
62            </div>
63            <div class="col-sm-4">
64              <img src="img/phone.png" class="w-100 rounded-circle" >
65            </div>
66          </div>
67
68          <div class="row">
69            <div class="col-sm-8 order-sm-2">
70              <h3>Awesome</h3>
71              <p>Hello. Hello. Hello. Hello. Hello. Hello. Hello.
72              Hello. Hello. Hello. Hello. Hello. Hello. </p>
73            </div>
74            <div class="col-sm-4 order-sm-1">
75              <img src="img/movie.png" class="w-100 rounded-circle" >
76            </div>
77          </div>
78        </div>
79      </section>
80
81      <section class="bg-light text-center py-5">
82        <h2 class="mb-5">Plans</h2>
83        <div class="container">
84          <table class="table table-hover">
85            <thead>
86              <tr><th>Plan A</th><th>Plan B</th></tr>
87            </thead>
88            <tbody>
89              <tr><td>AA</td><td>BB</td></tr>
90              <tr><td>AAA</td><td>BBB</td></tr>
91              <tr><td>AAAA</td><td>BBBB</td></tr>
92            </tbody>
93          </table>
94        </div>
95      </section>
96
97      <section class="py-5">
98        <h2 class="mb-5 text-center">How to use</h2>
99        <div class="container">
100          <ul class="nav nav-tabs">
101            <li class="nav-item"><a href="#ios" class="nav-link active" data-toggle="tab">iOS</a></li>
102            <li class="nav-item"><a href="android" class="nav-link" data-toggle="tab">Android</a></li>
103          </ul>
104          <div class="tab-content py-4">
105            <div id="ios" class="tab-pane active">
106              <p>Hello iOS. Hello iOS. Hello iOS. Hello iOS. Hello iOS. Hello iOS. Hello iOS.
107                Hello iOS. Hello iOS. </p>
108            </div>
109            <div id="android" class="tab-pane">
110              <p>Hello android. Hello android. Hello android. Hello android. Hello android. Hello android. Hello android.
111                  Hello android. Hello android. </p>
112            </div>
113          </div>
114        </div>
115      </section>
116    </main>
117    <footer>
118    </footer>
119
120    <!-- Optional JavaScript -->
121    <!-- jQuery first, then Popper.js, then Bootstrap JS -->
122    <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
123    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
124    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
125  </body>
126</html>
127