fix(theme): only show api sidebar button if page has api docs

Author: janvennemann

packages/vuepress/vuepress-theme-titanium/components/Navbar.vue

@@ -38,7 +38,7 @@
       <NavLinks class="can-hide"/>
     </div>
 
-    <ApiSidebarButton @toggle-api-sidebar="$emit('toggle-api-sidebar')"/>
+    <ApiSidebarButton v-if="$page.metadataKey" @toggle-api-sidebar="$emit('toggle-api-sidebar')"/>
   </header>
 </template>