Fix semantic-ui style conflict with v-cloak (#2722)

templates/repo/branch_dropdown.tmpl

@@ -16,7 +16,7 @@
 				<div class="item tag {{if eq $.BranchName .}}selected{{end}}" data-url="{{$.RepoLink}}/{{if $.PageIsCommits}}commits{{else}}src{{end}}/{{EscapePound .}}{{if $.TreePath}}/{{EscapePound $.TreePath}}{{end}}">{{.}}</div>
 			{{end}}
 		</div>
-		<div class="menu transition visible" v-if="menuVisible" v-cloak>
+		<div class="menu transition" :class="{visible: menuVisible}" v-if="menuVisible" v-cloak>
 			<div class="ui icon search input">
 				<i class="filter icon"></i>
 				<input name="search" ref="searchField" v-model="searchTerm" @keydown="keydown($event)" placeholder="{{.i18n.Tr "repo.filter_branch_and_tag"}}...">