Fix navbar dropdown (#19)

Author: sliao7

_includes/header.html

@@ -8,22 +8,16 @@
      <img src="{{ site.url }}{{ site.baseurl }}/favicon.ico" width="30" height="30" style="margin-right:5px" class="d-inline-block align-top" alt="">
       {{ site.title | escape }}
     </a>
-    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarColor02" aria-controls="navbarColor02" aria-expanded="false" aria-label="Toggle navigation">
+    <button class="toggler navbar-toggler collapsed" type="button" data-bs-toggle="collapse" data-bs-target="#navbarColor02" aria-controls="navbarColor02" aria-expanded="false" aria-label="Toggle navigation">
         <span class="navbar-toggler-icon"></span>
     </button>
 
     <div class="collapse navbar-collapse" id="navbarColor02">
-        <ul class="navbar-nav mr-auto">
-        <ul class="navbar-nav">
-          <li class="nav-item">
-              <a class="nav-link" href="{{ site.url }}{{ site.baseurl }}/">Home</a>
-          </li> 
-          {% for page in site.nav_pages %}
-           <li class="nav-item">
-            <a class="nav-link" href="{{ site.url }}{{ site.baseurl }}/{{page.name}}">{{page.name | capitalize }}</a>
-           </li> 
-          {% endfor %}
-        </ul>
-  </div>
+        <div class="navbar-nav mr-auto">
+            <a class="nav-item nav-link" href="{{ site.url }}{{ site.baseurl }}/">Home</a>
+            {% for page in site.nav_pages %}       
+                <a class="nav-item nav-link" href="{{ site.url }}{{ site.baseurl }}/{{page.name}}">{{page.name | capitalize }}</a>
+            {% endfor %}
+        </div>
+    </div>
 </nav>
-