Cleanup allocated resources explicitly upon validator exit (#146)

Now our debug builds use AddressSanitizer and it complains to memory
leaks.

Signed-off-by: Vladimir Krivopalov <vlkrivop@microsoft.com>

validator/main.c

@@ -40,5 +40,6 @@ int main(int argc, char* argv[])
         exit_with_error(err);
     }
 
+    modsecTerminate();
     exit(EXIT_SUCCESS);
 }