fix syntax error

templates/os/sources/sources.list.erb

@@ -21,9 +21,7 @@ deb     http://debian.stanford.edu/debian <%= @lsbdistcodename %> main non-free
 deb-src http://debian.stanford.edu/debian <%= @lsbdistcodename %> main non-free contrib
 <% end -%>
 <%-
-   if (@lsbdistcodename == 'wheezy')
-   or (@lsbdistcodename == 'jessie')
-   or (@lsbdistcodename == 'stretch')
+   if (@lsbdistcodename == 'wheezy') or (@lsbdistcodename == 'jessie') or (@lsbdistcodename == 'stretch')
 -%>
 
 # The archive that publishes updates for security vulnerabilities.