gluon-luci-admin: ensure that the authorized_keys file always ends with a newline

Fixes #558

package/gluon-luci-admin/files/usr/lib/lua/luci/model/cbi/admin/remote.lua

@@ -44,7 +44,7 @@ if fs.access("/etc/config/dropbear") then
 
   function keys.write(self, section, value)
     if value then
-      fs.writefile("/etc/dropbear/authorized_keys", value:gsub("\r\n", "\n"))
+      fs.writefile("/etc/dropbear/authorized_keys", value:gsub("\r\n", "\n"):trim() .. "\n")
     end
   end