Const modifiers

This functions do not change class variables
Would be good to mark them as const, so
class variables are not changed by coincidence

Change-Id: Iea34f6d26dbd1bde813035160e07ff2a681989e6
diff --git a/verifier.h b/verifier.h
index 6bee749..6fa8f2b 100644
--- a/verifier.h
+++ b/verifier.h
@@ -26,13 +26,13 @@
 #include <openssl/sha.h>
 
 struct RSADeleter {
-  void operator()(RSA* rsa) {
+  void operator()(RSA* rsa) const {
     RSA_free(rsa);
   }
 };
 
 struct ECKEYDeleter {
-  void operator()(EC_KEY* ec_key) {
+  void operator()(EC_KEY* ec_key) const {
     EC_KEY_free(ec_key);
   }
 };