Use unicode when adding a message

src/olympia/accounts/views.py

@@ -74,7 +74,7 @@ def login_user(request, user, identity):
         if not user.fxa_migrated():
             messages.success(
                 request,
-                _('Great job! You can now log in to Add-ons with your '
+                _(u'Great job! You can now log in to Add-ons with your '
                   'Firefox Account.'),
                 extra_tags='fxa')
         user.update(fxa_id=identity['uid'], email=identity['email'])