fix(theme): show version dropdown on versioned pages only

Author: janvennemann

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

@@ -20,7 +20,7 @@
       >{{ $siteTitle }}</span>
     </router-link>
 
-    <div v-if="hasVersions" class="versions-dropdown can-hide">
+    <div v-if="hasVersions && isVersionedPage" class="versions-dropdown can-hide">
       <DropdownLink :item="versionsDropdown"/>
     </div>
 
@@ -88,6 +88,10 @@ export default {
       return this.$versions && this.$versions.length > 0
     },
 
+    isVersionedPage () {
+      return this.$page.version !== undefined
+    },
+
     versionsDropdown () {
       const themeConfig = this.$site.themeConfig
       const currentVersion = this.$versions[0]