Change if not to unless

Author: wvu

modules/exploits/windows/mssql/ms09_004_sp_replwritetovarbin_sqli.rb

@@ -259,7 +259,7 @@ def check
     # since we need to have credentials for this vuln, we just login and run a query
     # to get the version information
     version = mssql_query_version
-    if not version
+    unless version
       return Exploit::CheckCode::Safe
     end
     print_status("@@version returned:\n\t" + version)