Land rapid7#7651, nil fix for etherpad_duo_login

Author: wvu

modules/auxiliary/scanner/http/etherpad_duo_login.rb

@@ -58,7 +58,7 @@ def is_app_epaduo?
       return false
     end
 
-    if (res and res.code == 200 and res.headers['Server'].include?("EtherPAD") and res.body.include?("EtherPAD Duo"))
+    if (res and res.code == 200 and res.headers['Server'] =~ /EtherPAD/ and res.body.include?("EtherPAD Duo"))
       vprint_good("Running EtherPAD Duo application ...")
       return true
     else