Fix memory leak issue when opening the certificate file

Fix memory leak issue when opening the certificate file
Refer to details: https://github.com/openbmc/bmcweb/issues/195

Tested:
Check the number of open files in bmcweb via lsof command
$lsof -p {the pid of bmcweb} | grep REG |grep pem | wc -l
0

Signed-off-by: Alan Kuo <Alan_Kuo@quantatw.com>
Change-Id: Id05fc4f3e653f51c5f02212ad8f361c7e8091808
diff --git a/include/ssl_key_handler.hpp b/include/ssl_key_handler.hpp
index 24e40a4..42a284a 100644
--- a/include/ssl_key_handler.hpp
+++ b/include/ssl_key_handler.hpp
@@ -199,6 +199,7 @@
         X509_free(cert);
         return nullptr;
     }
+    BIO_free(certFileBio);
     return cert;
 }