Fixes avatar URL setting string

index.html

             <div class="arrow-up"></div>
             <input type="text" id="setDisplayName" data-i18n="[placeholder]settings.name" placeholder="Name">
             <input type="text" id="setEmail" placeholder="E-Mail">
-            <input type="text" id="setAvatarUrl" placeholder="Avatar URL" data-i18n="[placeholder]settings.avatar">
+            <input type="text" id="setAvatarUrl" placeholder="Avatar URL" data-i18n="[placeholder]settings.avatarUrl">
             <select id="languages_selectbox"></select>
             <div id = "startMutedOptions">
                 <label class = "startMutedLabel">