navigation.pug: Fix navigation

src/lib/pug/navigation.pug

@@ -1,24 +1,17 @@
-nav.navbar.navbar-inverse.navbar-static-top
-  .container-fluid
-    .navbar-header
-      //- The navbar toggle button for small displays.
-      button.navbar-toggle.collapsed(
+nav.navbar.navbar-expand-lg.navbar-dark.bg-dark
+  .container
+    a.navbar-brand(href="index.html") tlater
+    button.navbar-toggler(
       type="button",
       data-toggle="collapse",
       data-target="#navbar",
+      aria-controls="#navbar",
       aria-expanded="false",
-          aria-controls="navbar"
+      aria-label="Toggle navigation"
     )
-        span.sr-only Toggle navigation
-        span.icon-bar
-        span.icon-bar
-        span.icon-bar
+      span.navbar-toggler-icon
 
-      //- The page title
-      a.navbar-brand(href="#") tlater
-
-    //- The actual navbar items
     #navbar.navbar-collapse.collapse
-      ul.nav.navbar-nav
-        li: a(href="mail") E-Mail
-        li: a(href="https://www.github.com/TLATER") GitHub
+      ul.navbar-nav.mr-auto
+        li.nav-item: a.nav-link(href="mail.html") E-Mail
+        li.nav-item: a.nav-link(href="https://www.github.com/TLATER") GitHub